content: /*
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  /*
   * This file is available under and governed by the GNU General Public
   * License version 2 only, as published by the Free Software Foundation.
   * However, the following notice accompanied the original version of this
   * file:
   *
   * Written by Doug Lea with assistance from members of JCP JSR-166
   * Expert Group and released to the public domain, as explained at
   * http://creativecommons.org/publicdomain/zero/1.0/
   */
  
  package java.util.concurrent;
  
  import java.io.ObjectStreamField;
  import java.io.Serializable;
  import java.lang.reflect.ParameterizedType;
  import java.lang.reflect.Type;
  import java.util.AbstractMap;
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.Enumeration;
  import java.util.HashMap;
  import java.util.Hashtable;
  import java.util.Iterator;
  import java.util.Map;
  import java.util.NoSuchElementException;
  import java.util.Set;
  import java.util.Spliterator;
  import java.util.concurrent.atomic.AtomicReference;
  import java.util.concurrent.locks.LockSupport;
  import java.util.concurrent.locks.ReentrantLock;
  import java.util.function.BiConsumer;
  import java.util.function.BiFunction;
  import java.util.function.Consumer;
  import java.util.function.DoubleBinaryOperator;
  import java.util.function.Function;
  import java.util.function.IntBinaryOperator;
  import java.util.function.LongBinaryOperator;
  import java.util.function.Predicate;
  import java.util.function.ToDoubleBiFunction;
  import java.util.function.ToDoubleFunction;
  import java.util.function.ToIntBiFunction;
  import java.util.function.ToIntFunction;
  import java.util.function.ToLongBiFunction;
  import java.util.function.ToLongFunction;
  import java.util.stream.Stream;
  
  // BEGIN android-note
  // removed link to collections framework docs
  // END android-note
  
  /**
   * A hash table supporting full concurrency of retrievals and
   * high expected concurrency for updates. This class obeys the
   * same functional specification as {@link Hashtable}, and
   * includes versions of methods corresponding to each method of
   * {@code Hashtable}. However, even though all operations are
   * thread-safe, retrieval operations do <em>not</em> entail locking,
   * and there is <em>not</em> any support for locking the entire table
   * in a way that prevents all access.  This class is fully
   * interoperable with {@code Hashtable} in programs that rely on its
   * thread safety but not on its synchronization details.
   *
   * <p>Retrieval operations (including {@code get}) generally do not
   * block, so may overlap with update operations (including {@code put}
   * and {@code remove}). Retrievals reflect the results of the most
   * recently <em>completed</em> update operations holding upon their
   * onset. (More formally, an update operation for a given key bears a
   * <em>happens-before</em> relation with any (non-null) retrieval for
   * that key reporting the updated value.)  For aggregate operations
   * such as {@code putAll} and {@code clear}, concurrent retrievals may
   * reflect insertion or removal of only some entries.  Similarly,
   * Iterators, Spliterators and Enumerations return elements reflecting the
   * state of the hash table at some point at or since the creation of the
   * iterator/enumeration.  They do <em>not</em> throw {@link
   * java.util.ConcurrentModificationException ConcurrentModificationException}.
   * However, iterators are designed to be used by only one thread at a time.
   * Bear in mind that the results of aggregate status methods including
   * {@code size}, {@code isEmpty}, and {@code containsValue} are typically
   * useful only when a map is not undergoing concurrent updates in other threads.
   * Otherwise the results of these methods reflect transient states
   * that may be adequate for monitoring or estimation purposes, but not
   * for program control.
   *
   * <p>The table is dynamically expanded when there are too many
   * collisions (i.e., keys that have distinct hash codes but fall into
   * the same slot modulo the table size), with the expected average
   * effect of maintaining roughly two bins per mapping (corresponding
   * to a 0.75 load factor threshold for resizing). There may be much
   * variance around this average as mappings are added and removed, but
   * overall, this maintains a commonly accepted time/space tradeoff for
   * hash tables.  However, resizing this or any other kind of hash
   * table may be a relatively slow operation. When possible, it is a
   * good idea to provide a size estimate as an optional {@code
   * initialCapacity} constructor argument. An additional optional
   * {@code loadFactor} constructor argument provides a further means of
   * customizing initial table capacity by specifying the table density
   * to be used in calculating the amount of space to allocate for the
   * given number of elements.  Also, for compatibility with previous
   * versions of this class, constructors may optionally specify an
   * expected {@code concurrencyLevel} as an additional hint for
   * internal sizing.  Note that using many keys with exactly the same
   * {@code hashCode()} is a sure way to slow down performance of any
   * hash table. To ameliorate impact, when keys are {@link Comparable},
   * this class may use comparison order among keys to help break ties.
   *
   * <p>A {@link Set} projection of a ConcurrentHashMap may be created
   * (using {@link #newKeySet()} or {@link #newKeySet(int)}), or viewed
   * (using {@link #keySet(Object)} when only keys are of interest, and the
   * mapped values are (perhaps transiently) not used or all take the
   * same mapping value.
   *
   * <p>A ConcurrentHashMap can be used as a scalable frequency map (a
   * form of histogram or multiset) by using {@link
   * java.util.concurrent.atomic.LongAdder} values and initializing via
   * {@link #computeIfAbsent computeIfAbsent}. For example, to add a count
   * to a {@code ConcurrentHashMap<String,LongAdder> freqs}, you can use
   * {@code freqs.computeIfAbsent(key, k -> new LongAdder()).increment();}
   *
   * <p>This class and its views and iterators implement all of the
   * <em>optional</em> methods of the {@link Map} and {@link Iterator}
   * interfaces.
   *
   * <p>Like {@link Hashtable} but unlike {@link HashMap}, this class
   * does <em>not</em> allow {@code null} to be used as a key or value.
   *
   * <p>ConcurrentHashMaps support a set of sequential and parallel bulk
   * operations that, unlike most {@link Stream} methods, are designed
   * to be safely, and often sensibly, applied even with maps that are
   * being concurrently updated by other threads; for example, when
   * computing a snapshot summary of the values in a shared registry.
   * There are three kinds of operation, each with four forms, accepting
   * functions with keys, values, entries, and (key, value) pairs as
   * arguments and/or return values. Because the elements of a
   * ConcurrentHashMap are not ordered in any particular way, and may be
   * processed in different orders in different parallel executions, the
   * correctness of supplied functions should not depend on any
   * ordering, or on any other objects or values that may transiently
   * change while computation is in progress; and except for forEach
   * actions, should ideally be side-effect-free. Bulk operations on
   * {@link Entry} objects do not support method {@code
   * setValue}.
   *
   * <ul>
   * <li>forEach: Performs a given action on each element.
   * A variant form applies a given transformation on each element
   * before performing the action.
   *
   * <li>search: Returns the first available non-null result of
   * applying a given function on each element; skipping further
   * search when a result is found.
   *
   * <li>reduce: Accumulates each element.  The supplied reduction
   * function cannot rely on ordering (more formally, it should be
   * both associative and commutative).  There are five variants:
   *
   * <ul>
   *
   * <li>Plain reductions. (There is not a form of this method for
   * (key, value) function arguments since there is no corresponding
   * return type.)
   *
   * <li>Mapped reductions that accumulate the results of a given
   * function applied to each element.
   *
   * <li>Reductions to scalar doubles, longs, and ints, using a
   * given basis value.
   *
   * </ul>
   * </ul>
   *
   * <p>These bulk operations accept a {@code parallelismThreshold}
   * argument. Methods proceed sequentially if the current map size is
   * estimated to be less than the given threshold. Using a value of
   * {@code Long.MAX_VALUE} suppresses all parallelism.  Using a value
   * of {@code 1} results in maximal parallelism by partitioning into
   * enough subtasks to fully utilize the {@link
   * ForkJoinPool#commonPool()} that is used for all parallel
   * computations. Normally, you would initially choose one of these
   * extreme values, and then measure performance of using in-between
   * values that trade off overhead versus throughput.
   *
   * <p>The concurrency properties of bulk operations follow
   * from those of ConcurrentHashMap: Any non-null result returned
   * from {@code get(key)} and related access methods bears a
   * happens-before relation with the associated insertion or
   * update.  The result of any bulk operation reflects the
   * composition of these per-element relations (but is not
   * necessarily atomic with respect to the map as a whole unless it
   * is somehow known to be quiescent).  Conversely, because keys
   * and values in the map are never null, null serves as a reliable
   * atomic indicator of the current lack of any result.  To
   * maintain this property, null serves as an implicit basis for
   * all non-scalar reduction operations. For the double, long, and
   * int versions, the basis should be one that, when combined with
   * any other value, returns that other value (more formally, it
   * should be the identity element for the reduction). Most common
   * reductions have these properties; for example, computing a sum
   * with basis 0 or a minimum with basis MAX_VALUE.
   *
   * <p>Search and transformation functions provided as arguments
   * should similarly return null to indicate the lack of any result
   * (in which case it is not used). In the case of mapped
   * reductions, this also enables transformations to serve as
   * filters, returning null (or, in the case of primitive
   * specializations, the identity basis) if the element should not
   * be combined. You can create compound transformations and
   * filterings by composing them yourself under this "null means
   * there is nothing there now" rule before using them in search or
   * reduce operations.
   *
   * <p>Methods accepting and/or returning Entry arguments maintain
   * key-value associations. They may be useful for example when
   * finding the key for the greatest value. Note that "plain" Entry
   * arguments can be supplied using {@code new
   * AbstractMap.SimpleEntry(k,v)}.
   *
   * <p>Bulk operations may complete abruptly, throwing an
   * exception encountered in the application of a supplied
   * function. Bear in mind when handling such exceptions that other
   * concurrently executing functions could also have thrown
   * exceptions, or would have done so if the first exception had
   * not occurred.
   *
   * <p>Speedups for parallel compared to sequential forms are common
   * but not guaranteed.  Parallel operations involving brief functions
   * on small maps may execute more slowly than sequential forms if the
   * underlying work to parallelize the computation is more expensive
   * than the computation itself.  Similarly, parallelization may not
   * lead to much actual parallelism if all processors are busy
   * performing unrelated tasks.
   *
   * <p>All arguments to all task methods must be non-null.
   *
   * @since 1.5
   * @author Doug Lea
   * @param <K> the type of keys maintained by this map
   * @param <V> the type of mapped values
   */
  public class ConcurrentHashMap<K,V> extends AbstractMap<K,V>
      implements ConcurrentMap<K,V>, Serializable {
      private static final long serialVersionUID = 7249069246763182397L;
  
      /*
       * Overview:
       *
       * The primary design goal of this hash table is to maintain
       * concurrent readability (typically method get(), but also
       * iterators and related methods) while minimizing update
       * contention. Secondary goals are to keep space consumption about
       * the same or better than java.util.HashMap, and to support high
       * initial insertion rates on an empty table by many threads.
       *
       * This map usually acts as a binned (bucketed) hash table.  Each
       * key-value mapping is held in a Node.  Most nodes are instances
       * of the basic Node class with hash, key, value, and next
       * fields. However, various subclasses exist: TreeNodes are
       * arranged in balanced trees, not lists.  TreeBins hold the roots
       * of sets of TreeNodes. ForwardingNodes are placed at the heads
       * of bins during resizing. ReservationNodes are used as
       * placeholders while establishing values in computeIfAbsent and
       * related methods.  The types TreeBin, ForwardingNode, and
       * ReservationNode do not hold normal user keys, values, or
       * hashes, and are readily distinguishable during search etc
       * because they have negative hash fields and null key and value
       * fields. (These special nodes are either uncommon or transient,
       * so the impact of carrying around some unused fields is
       * insignificant.)
       *
       * The table is lazily initialized to a power-of-two size upon the
       * first insertion.  Each bin in the table normally contains a
       * list of Nodes (most often, the list has only zero or one Node).
       * Table accesses require volatile/atomic reads, writes, and
       * CASes.  Because there is no other way to arrange this without
       * adding further indirections, we use intrinsics
       * (sun.misc.Unsafe) operations.
       *
       * We use the top (sign) bit of Node hash fields for control
       * purposes -- it is available anyway because of addressing
       * constraints.  Nodes with negative hash fields are specially
       * handled or ignored in map methods.
       *
       * Insertion (via put or its variants) of the first node in an
       * empty bin is performed by just CASing it to the bin.  This is
       * by far the most common case for put operations under most
       * key/hash distributions.  Other update operations (insert,
       * delete, and replace) require locks.  We do not want to waste
       * the space required to associate a distinct lock object with
       * each bin, so instead use the first node of a bin list itself as
       * a lock. Locking support for these locks relies on builtin
       * "synchronized" monitors.
       *
       * Using the first node of a list as a lock does not by itself
       * suffice though: When a node is locked, any update must first
       * validate that it is still the first node after locking it, and
       * retry if not. Because new nodes are always appended to lists,
       * once a node is first in a bin, it remains first until deleted
       * or the bin becomes invalidated (upon resizing).
       *
       * The main disadvantage of per-bin locks is that other update
       * operations on other nodes in a bin list protected by the same
       * lock can stall, for example when user equals() or mapping
       * functions take a long time.  However, statistically, under
       * random hash codes, this is not a common problem.  Ideally, the
       * frequency of nodes in bins follows a Poisson distribution
       * (http://en.wikipedia.org/wiki/Poisson_distribution) with a
       * parameter of about 0.5 on average, given the resizing threshold
       * of 0.75, although with a large variance because of resizing
       * granularity. Ignoring variance, the expected occurrences of
       * list size k are (exp(-0.5) * pow(0.5, k) / factorial(k)). The
       * first values are:
       *
       * 0:    0.60653066
       * 1:    0.30326533
       * 2:    0.07581633
       * 3:    0.01263606
       * 4:    0.00157952
       * 5:    0.00015795
       * 6:    0.00001316
       * 7:    0.00000094
       * 8:    0.00000006
       * more: less than 1 in ten million
       *
       * Lock contention probability for two threads accessing distinct
       * elements is roughly 1 / (8 * #elements) under random hashes.
       *
       * Actual hash code distributions encountered in practice
       * sometimes deviate significantly from uniform randomness.  This
       * includes the case when N > (1<<30), so some keys MUST collide.
       * Similarly for dumb or hostile usages in which multiple keys are
       * designed to have identical hash codes or ones that differs only
       * in masked-out high bits. So we use a secondary strategy that
       * applies when the number of nodes in a bin exceeds a
       * threshold. These TreeBins use a balanced tree to hold nodes (a
       * specialized form of red-black trees), bounding search time to
       * O(log N).  Each search step in a TreeBin is at least twice as
       * slow as in a regular list, but given that N cannot exceed
       * (1<<64) (before running out of addresses) this bounds search
       * steps, lock hold times, etc, to reasonable constants (roughly
       * 100 nodes inspected per operation worst case) so long as keys
       * are Comparable (which is very common -- String, Long, etc).
       * TreeBin nodes (TreeNodes) also maintain the same "next"
       * traversal pointers as regular nodes, so can be traversed in
       * iterators in the same way.
       *
       * The table is resized when occupancy exceeds a percentage
       * threshold (nominally, 0.75, but see below).  Any thread
       * noticing an overfull bin may assist in resizing after the
       * initiating thread allocates and sets up the replacement array.
       * However, rather than stalling, these other threads may proceed
       * with insertions etc.  The use of TreeBins shields us from the
       * worst case effects of overfilling while resizes are in
       * progress.  Resizing proceeds by transferring bins, one by one,
       * from the table to the next table. However, threads claim small
       * blocks of indices to transfer (via field transferIndex) before
       * doing so, reducing contention.  A generation stamp in field
       * sizeCtl ensures that resizings do not overlap. Because we are
       * using power-of-two expansion, the elements from each bin must
       * either stay at same index, or move with a power of two
       * offset. We eliminate unnecessary node creation by catching
       * cases where old nodes can be reused because their next fields
       * won't change.  On average, only about one-sixth of them need
       * cloning when a table doubles. The nodes they replace will be
       * garbage collectable as soon as they are no longer referenced by
       * any reader thread that may be in the midst of concurrently
       * traversing table.  Upon transfer, the old table bin contains
       * only a special forwarding node (with hash field "MOVED") that
       * contains the next table as its key. On encountering a
       * forwarding node, access and update operations restart, using
       * the new table.
       *
       * Each bin transfer requires its bin lock, which can stall
       * waiting for locks while resizing. However, because other
       * threads can join in and help resize rather than contend for
       * locks, average aggregate waits become shorter as resizing
       * progresses.  The transfer operation must also ensure that all
       * accessible bins in both the old and new table are usable by any
       * traversal.  This is arranged in part by proceeding from the
       * last bin (table.length - 1) up towards the first.  Upon seeing
       * a forwarding node, traversals (see class Traverser) arrange to
       * move to the new table without revisiting nodes.  To ensure that
       * no intervening nodes are skipped even when moved out of order,
       * a stack (see class TableStack) is created on first encounter of
       * a forwarding node during a traversal, to maintain its place if
       * later processing the current table. The need for these
       * save/restore mechanics is relatively rare, but when one
       * forwarding node is encountered, typically many more will be.
       * So Traversers use a simple caching scheme to avoid creating so
       * many new TableStack nodes. (Thanks to Peter Levart for
       * suggesting use of a stack here.)
       *
       * The traversal scheme also applies to partial traversals of
       * ranges of bins (via an alternate Traverser constructor)
       * to support partitioned aggregate operations.  Also, read-only
       * operations give up if ever forwarded to a null table, which
       * provides support for shutdown-style clearing, which is also not
       * currently implemented.
       *
       * Lazy table initialization minimizes footprint until first use,
       * and also avoids resizings when the first operation is from a
       * putAll, constructor with map argument, or deserialization.
       * These cases attempt to override the initial capacity settings,
       * but harmlessly fail to take effect in cases of races.
       *
       * The element count is maintained using a specialization of
       * LongAdder. We need to incorporate a specialization rather than
       * just use a LongAdder in order to access implicit
       * contention-sensing that leads to creation of multiple
       * CounterCells.  The counter mechanics avoid contention on
       * updates but can encounter cache thrashing if read too
       * frequently during concurrent access. To avoid reading so often,
       * resizing under contention is attempted only upon adding to a
       * bin already holding two or more nodes. Under uniform hash
       * distributions, the probability of this occurring at threshold
       * is around 13%, meaning that only about 1 in 8 puts check
       * threshold (and after resizing, many fewer do so).
       *
       * TreeBins use a special form of comparison for search and
       * related operations (which is the main reason we cannot use
       * existing collections such as TreeMaps). TreeBins contain
       * Comparable elements, but may contain others, as well as
       * elements that are Comparable but not necessarily Comparable for
       * the same T, so we cannot invoke compareTo among them. To handle
       * this, the tree is ordered primarily by hash value, then by
       * Comparable.compareTo order if applicable.  On lookup at a node,
       * if elements are not comparable or compare as 0 then both left
       * and right children may need to be searched in the case of tied
       * hash values. (This corresponds to the full list search that
       * would be necessary if all elements were non-Comparable and had
       * tied hashes.) On insertion, to keep a total ordering (or as
       * close as is required here) across rebalancings, we compare
       * classes and identityHashCodes as tie-breakers. The red-black
       * balancing code is updated from pre-jdk-collections
       * (http://gee.cs.oswego.edu/dl/classes/collections/RBCell.java)
       * based in turn on Cormen, Leiserson, and Rivest "Introduction to
       * Algorithms" (CLR).
       *
       * TreeBins also require an additional locking mechanism.  While
       * list traversal is always possible by readers even during
       * updates, tree traversal is not, mainly because of tree-rotations
       * that may change the root node and/or its linkages.  TreeBins
       * include a simple read-write lock mechanism parasitic on the
       * main bin-synchronization strategy: Structural adjustments
       * associated with an insertion or removal are already bin-locked
       * (and so cannot conflict with other writers) but must wait for
       * ongoing readers to finish. Since there can be only one such
       * waiter, we use a simple scheme using a single "waiter" field to
       * block writers.  However, readers need never block.  If the root
       * lock is held, they proceed along the slow traversal path (via
       * next-pointers) until the lock becomes available or the list is
       * exhausted, whichever comes first. These cases are not fast, but
       * maximize aggregate expected throughput.
       *
       * Maintaining API and serialization compatibility with previous
       * versions of this class introduces several oddities. Mainly: We
       * leave untouched but unused constructor arguments referring to
       * concurrencyLevel. We accept a loadFactor constructor argument,
       * but apply it only to initial table capacity (which is the only
       * time that we can guarantee to honor it.) We also declare an
       * unused "Segment" class that is instantiated in minimal form
       * only when serializing.
       *
       * Also, solely for compatibility with previous versions of this
       * class, it extends AbstractMap, even though all of its methods
       * are overridden, so it is just useless baggage.
       *
       * This file is organized to make things a little easier to follow
       * while reading than they might otherwise: First the main static
       * declarations and utilities, then fields, then main public
       * methods (with a few factorings of multiple public methods into
       * internal ones), then sizing methods, trees, traversers, and
       * bulk operations.
       */
  
      /* ---------------- Constants -------------- */
  
      /**
       * The largest possible table capacity.  This value must be
       * exactly 1<<30 to stay within Java array allocation and indexing
       * bounds for power of two table sizes, and is further required
       * because the top two bits of 32bit hash fields are used for
       * control purposes.
       */
      private static final int MAXIMUM_CAPACITY = 1 << 30;
  
      /**
       * The default initial table capacity.  Must be a power of 2
       * (i.e., at least 1) and at most MAXIMUM_CAPACITY.
       */
      private static final int DEFAULT_CAPACITY = 16;
  
      /**
       * The largest possible (non-power of two) array size.
       * Needed by toArray and related methods.
       */
      static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
  
      /**
       * The default concurrency level for this table. Unused but
       * defined for compatibility with previous versions of this class.
       */
      private static final int DEFAULT_CONCURRENCY_LEVEL = 16;
  
      /**
       * The load factor for this table. Overrides of this value in
       * constructors affect only the initial table capacity.  The
       * actual floating point value isn't normally used -- it is
       * simpler to use expressions such as {@code n - (n >>> 2)} for
       * the associated resizing threshold.
       */
      private static final float LOAD_FACTOR = 0.75f;
  
      /**
       * The bin count threshold for using a tree rather than list for a
       * bin.  Bins are converted to trees when adding an element to a
       * bin with at least this many nodes. The value must be greater
       * than 2, and should be at least 8 to mesh with assumptions in
       * tree removal about conversion back to plain bins upon
       * shrinkage.
       */
      static final int TREEIFY_THRESHOLD = 8;
  
      /**
       * The bin count threshold for untreeifying a (split) bin during a
       * resize operation. Should be less than TREEIFY_THRESHOLD, and at
       * most 6 to mesh with shrinkage detection under removal.
       */
      static final int UNTREEIFY_THRESHOLD = 6;
  
      /**
       * The smallest table capacity for which bins may be treeified.
       * (Otherwise the table is resized if too many nodes in a bin.)
       * The value should be at least 4 * TREEIFY_THRESHOLD to avoid
       * conflicts between resizing and treeification thresholds.
       */
      static final int MIN_TREEIFY_CAPACITY = 64;
  
      /**
       * Minimum number of rebinnings per transfer step. Ranges are
       * subdivided to allow multiple resizer threads.  This value
       * serves as a lower bound to avoid resizers encountering
       * excessive memory contention.  The value should be at least
       * DEFAULT_CAPACITY.
       */
      private static final int MIN_TRANSFER_STRIDE = 16;
  
      /**
       * The number of bits used for generation stamp in sizeCtl.
       * Must be at least 6 for 32bit arrays.
       */
      private static final int RESIZE_STAMP_BITS = 16;
  
      /**
       * The maximum number of threads that can help resize.
       * Must fit in 32 - RESIZE_STAMP_BITS bits.
       */
      private static final int MAX_RESIZERS = (1 << (32 - RESIZE_STAMP_BITS)) - 1;
  
      /**
       * The bit shift for recording size stamp in sizeCtl.
       */
      private static final int RESIZE_STAMP_SHIFT = 32 - RESIZE_STAMP_BITS;
  
      /*
       * Encodings for Node hash fields. See above for explanation.
       */
      static final int MOVED     = -1; // hash for forwarding nodes
      static final int TREEBIN   = -2; // hash for roots of trees
      static final int RESERVED  = -3; // hash for transient reservations
      static final int HASH_BITS = 0x7fffffff; // usable bits of normal node hash
  
      /** Number of CPUS, to place bounds on some sizings */
      static final int NCPU = Runtime.getRuntime().availableProcessors();
  
      /**
       * Serialized pseudo-fields, provided only for jdk7 compatibility.
       * @serialField segments Segment[]
       *   The segments, each of which is a specialized hash table.
       * @serialField segmentMask int
       *   Mask value for indexing into segments. The upper bits of a
       *   key's hash code are used to choose the segment.
       * @serialField segmentShift int
       *   Shift value for indexing within segments.
       */
      private static final ObjectStreamField[] serialPersistentFields = {
          new ObjectStreamField("segments", Segment[].class),
          new ObjectStreamField("segmentMask", Integer.TYPE),
          new ObjectStreamField("segmentShift", Integer.TYPE),
      };
  
      /* ---------------- Nodes -------------- */
  
      /**
       * Key-value entry.  This class is never exported out as a
       * user-mutable Map.Entry (i.e., one supporting setValue; see
       * MapEntry below), but can be used for read-only traversals used
       * in bulk tasks.  Subclasses of Node with a negative hash field
       * are special, and contain null keys and values (but are never
       * exported).  Otherwise, keys and vals are never null.
       */
      static class Node<K,V> implements Entry<K,V> {
          final int hash;
          final K key;
          volatile V val;
          volatile Node<K,V> next;
  
          Node(int hash, K key, V val, Node<K,V> next) {
              this.hash = hash;
              this.key = key;
              this.val = val;
              this.next = next;
          }
  
          public final K getKey()     { return key; }
          public final V getValue()   { return val; }
          public final int hashCode() { return key.hashCode() ^ val.hashCode(); }
          public final String toString() {
              return Helpers.mapEntryToString(key, val);
          }
          public final V setValue(V value) {
              throw new UnsupportedOperationException();
          }
  
          public final boolean equals(Object o) {
              Object k, v, u; Entry<?,?> e;
              return ((o instanceof Map.Entry) &&
                      (k = (e = (Entry<?,?>)o).getKey()) != null &&
                      (v = e.getValue()) != null &&
                      (k == key || k.equals(key)) &&
                      (v == (u = val) || v.equals(u)));
          }
  
          /**
           * Virtualized support for map.get(); overridden in subclasses.
           */
          Node<K,V> find(int h, Object k) {
              Node<K,V> e = this;
              if (k != null) {
                  do {
                      K ek;
                      if (e.hash == h &&
                          ((ek = e.key) == k || (ek != null && k.equals(ek))))
                          return e;
                  } while ((e = e.next) != null);
              }
              return null;
          }
      }
  
      /* ---------------- Static utilities -------------- */
  
      /**
       * Spreads (XORs) higher bits of hash to lower and also forces top
       * bit to 0. Because the table uses power-of-two masking, sets of
       * hashes that vary only in bits above the current mask will
       * always collide. (Among known examples are sets of Float keys
       * holding consecutive whole numbers in small tables.)  So we
       * apply a transform that spreads the impact of higher bits
       * downward. There is a tradeoff between speed, utility, and
       * quality of bit-spreading. Because many common sets of hashes
       * are already reasonably distributed (so don't benefit from
       * spreading), and because we use trees to handle large sets of
       * collisions in bins, we just XOR some shifted bits in the
       * cheapest possible way to reduce systematic lossage, as well as
       * to incorporate impact of the highest bits that would otherwise
       * never be used in index calculations because of table bounds.
       */
      static final int spread(int h) {
          return (h ^ (h >>> 16)) & HASH_BITS;
      }
  
      /**
       * Returns a power of two table size for the given desired capacity.
       * See Hackers Delight, sec 3.2
       */
      private static final int tableSizeFor(int c) {
          int n = c - 1;
          n |= n >>> 1;
          n |= n >>> 2;
          n |= n >>> 4;
          n |= n >>> 8;
          n |= n >>> 16;
          return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
      }
  
      /**
       * Returns x's Class if it is of the form "class C implements
       * Comparable<C>", else null.
       */
      static Class<?> comparableClassFor(Object x) {
          if (x instanceof Comparable) {
              Class<?> c; Type[] ts, as; Type t; ParameterizedType p;
              if ((c = x.getClass()) == String.class) // bypass checks
                  return c;
              if ((ts = c.getGenericInterfaces()) != null) {
                  for (int i = 0; i < ts.length; ++i) {
                      if (((t = ts[i]) instanceof ParameterizedType) &&
                          ((p = (ParameterizedType)t).getRawType() ==
                           Comparable.class) &&
                          (as = p.getActualTypeArguments()) != null &&
                          as.length == 1 && as[0] == c) // type arg is c
                          return c;
                  }
              }
          }
          return null;
      }
  
      /**
       * Returns k.compareTo(x) if x matches kc (k's screened comparable
       * class), else 0.
       */
      @SuppressWarnings({"rawtypes","unchecked"}) // for cast to Comparable
      static int compareComparables(Class<?> kc, Object k, Object x) {
          return (x == null || x.getClass() != kc ? 0 :
                  ((Comparable)k).compareTo(x));
      }
  
      /* ---------------- Table element access -------------- */
  
      /*
       * Volatile access methods are used for table elements as well as
       * elements of in-progress next table while resizing.  All uses of
       * the tab arguments must be null checked by callers.  All callers
       * also paranoically precheck that tab's length is not zero (or an
       * equivalent check), thus ensuring that any index argument taking
       * the form of a hash value anded with (length - 1) is a valid
       * index.  Note that, to be correct wrt arbitrary concurrency
       * errors by users, these checks must operate on local variables,
       * which accounts for some odd-looking inline assignments below.
       * Note that calls to setTabAt always occur within locked regions,
       * and so in principle require only release ordering, not
       * full volatile semantics, but are currently coded as volatile
       * writes to be conservative.
       */
  
      @SuppressWarnings("unchecked")
      static final <K,V> Node<K,V> tabAt(Node<K,V>[] tab, int i) {
          return (Node<K,V>)U.getObjectVolatile(tab, ((long)i << ASHIFT) + ABASE);
      }
  
      static final <K,V> boolean casTabAt(Node<K,V>[] tab, int i,
                                          Node<K,V> c, Node<K,V> v) {
          return U.compareAndSwapObject(tab, ((long)i << ASHIFT) + ABASE, c, v);
      }
  
      static final <K,V> void setTabAt(Node<K,V>[] tab, int i, Node<K,V> v) {
          U.putObjectVolatile(tab, ((long)i << ASHIFT) + ABASE, v);
      }
  
      /* ---------------- Fields -------------- */
  
      /**
       * The array of bins. Lazily initialized upon first insertion.
       * Size is always a power of two. Accessed directly by iterators.
       */
      transient volatile Node<K,V>[] table;
  
      /**
       * The next table to use; non-null only while resizing.
       */
      private transient volatile Node<K,V>[] nextTable;
  
      /**
       * Base counter value, used mainly when there is no contention,
       * but also as a fallback during table initialization
       * races. Updated via CAS.
       */
      private transient volatile long baseCount;
  
      /**
       * Table initialization and resizing control.  When negative, the
       * table is being initialized or resized: -1 for initialization,
       * else -(1 + the number of active resizing threads).  Otherwise,
       * when table is null, holds the initial table size to use upon
       * creation, or 0 for default. After initialization, holds the
       * next element count value upon which to resize the table.
       */
      private transient volatile int sizeCtl;
  
      /**
       * The next table index (plus one) to split while resizing.
       */
      private transient volatile int transferIndex;
  
      /**
       * Spinlock (locked via CAS) used when resizing and/or creating CounterCells.
       */
      private transient volatile int cellsBusy;
  
      /**
       * Table of counter cells. When non-null, size is a power of 2.
       */
      private transient volatile CounterCell[] counterCells;
  
      // views
      private transient KeySetView<K,V> keySet;
      private transient ValuesView<K,V> values;
      private transient EntrySetView<K,V> entrySet;
  
  
      /* ---------------- Public operations -------------- */
  
      /**
       * Creates a new, empty map with the default initial table size (16).
       */
      public ConcurrentHashMap() {
      }
  
      /**
       * Creates a new, empty map with an initial table size
       * accommodating the specified number of elements without the need
       * to dynamically resize.
       *
       * @param initialCapacity The implementation performs internal
       * sizing to accommodate this many elements.
       * @throws IllegalArgumentException if the initial capacity of
       * elements is negative
       */
      public ConcurrentHashMap(int initialCapacity) {
          if (initialCapacity < 0)
              throw new IllegalArgumentException();
          int cap = ((initialCapacity >= (MAXIMUM_CAPACITY >>> 1)) ?
                     MAXIMUM_CAPACITY :
                     tableSizeFor(initialCapacity + (initialCapacity >>> 1) + 1));
          this.sizeCtl = cap;
      }
  
      /**
       * Creates a new map with the same mappings as the given map.
       *
       * @param m the map
       */
      public ConcurrentHashMap(Map<? extends K, ? extends V> m) {
          this.sizeCtl = DEFAULT_CAPACITY;
          putAll(m);
      }
  
      /**
       * Creates a new, empty map with an initial table size based on
       * the given number of elements ({@code initialCapacity}) and
       * initial table density ({@code loadFactor}).
       *
       * @param initialCapacity the initial capacity. The implementation
       * performs internal sizing to accommodate this many elements,
       * given the specified load factor.
       * @param loadFactor the load factor (table density) for
       * establishing the initial table size
       * @throws IllegalArgumentException if the initial capacity of
       * elements is negative or the load factor is nonpositive
       *
       * @since 1.6
       */
      public ConcurrentHashMap(int initialCapacity, float loadFactor) {
          this(initialCapacity, loadFactor, 1);
      }
  
      /**
       * Creates a new, empty map with an initial table size based on
       * the given number of elements ({@code initialCapacity}), table
       * density ({@code loadFactor}), and number of concurrently
       * updating threads ({@code concurrencyLevel}).
       *
       * @param initialCapacity the initial capacity. The implementation
       * performs internal sizing to accommodate this many elements,
       * given the specified load factor.
       * @param loadFactor the load factor (table density) for
       * establishing the initial table size
       * @param concurrencyLevel the estimated number of concurrently
       * updating threads. The implementation may use this value as
       * a sizing hint.
       * @throws IllegalArgumentException if the initial capacity is
       * negative or the load factor or concurrencyLevel are
       * nonpositive
       */
      public ConcurrentHashMap(int initialCapacity,
                               float loadFactor, int concurrencyLevel) {
          if (!(loadFactor > 0.0f) || initialCapacity < 0 || concurrencyLevel <= 0)
              throw new IllegalArgumentException();
          if (initialCapacity < concurrencyLevel)   // Use at least as many bins
              initialCapacity = concurrencyLevel;   // as estimated threads
          long size = (long)(1.0 + (long)initialCapacity / loadFactor);
          int cap = (size >= (long)MAXIMUM_CAPACITY) ?
              MAXIMUM_CAPACITY : tableSizeFor((int)size);
          this.sizeCtl = cap;
      }
  
      // Original (since JDK1.2) Map methods
  
      /**
       * {@inheritDoc}
       */
      public int size() {
          long n = sumCount();
          return ((n < 0L) ? 0 :
                  (n > (long)Integer.MAX_VALUE) ? Integer.MAX_VALUE :
                  (int)n);
      }
  
      /**
       * {@inheritDoc}
       */
      public boolean isEmpty() {
          return sumCount() <= 0L; // ignore transient negative values
      }
  
      /**
       * Returns the value to which the specified key is mapped,
       * or {@code null} if this map contains no mapping for the key.
       *
       * <p>More formally, if this map contains a mapping from a key
       * {@code k} to a value {@code v} such that {@code key.equals(k)},
       * then this method returns {@code v}; otherwise it returns
       * {@code null}.  (There can be at most one such mapping.)
       *
       * @throws NullPointerException if the specified key is null
       */
      public V get(Object key) {
          Node<K,V>[] tab; Node<K,V> e, p; int n, eh; K ek;
          int h = spread(key.hashCode());
          if ((tab = table) != null && (n = tab.length) > 0 &&
              (e = tabAt(tab, (n - 1) & h)) != null) {
              if ((eh = e.hash) == h) {
                  if ((ek = e.key) == key || (ek != null && key.equals(ek)))
                      return e.val;
              }
              else if (eh < 0)
                  return (p = e.find(h, key)) != null ? p.val : null;
              while ((e = e.next) != null) {
                  if (e.hash == h &&
                      ((ek = e.key) == key || (ek != null && key.equals(ek))))
                      return e.val;
              }
          }
          return null;
      }
  
      /**
       * Tests if the specified object is a key in this table.
       *
       * @param  key possible key
       * @return {@code true} if and only if the specified object
       *         is a key in this table, as determined by the
       *         {@code equals} method; {@code false} otherwise
       * @throws NullPointerException if the specified key is null
       */
      public boolean containsKey(Object key) {
          return get(key) != null;
      }
  
      /**
       * Returns {@code true} if this map maps one or more keys to the
       * specified value. Note: This method may require a full traversal
       * of the map, and is much slower than method {@code containsKey}.
       *
       * @param value value whose presence in this map is to be tested
       * @return {@code true} if this map maps one or more keys to the
       *         specified value
       * @throws NullPointerException if the specified value is null
       */
      public boolean containsValue(Object value) {
          if (value == null)
              throw new NullPointerException();
          Node<K,V>[] t;
          if ((t = table) != null) {
              Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
              for (Node<K,V> p; (p = it.advance()) != null; ) {
                  V v;
                  if ((v = p.val) == value || (v != null && value.equals(v)))
                      return true;
              }
          }
          return false;
      }
  
      /**
       * Maps the specified key to the specified value in this table.
       * Neither the key nor the value can be null.
       *
       * <p>The value can be retrieved by calling the {@code get} method
       * with a key that is equal to the original key.
       *
       * @param key key with which the specified value is to be associated
       * @param value value to be associated with the specified key
       * @return the previous value associated with {@code key}, or
       *         {@code null} if there was no mapping for {@code key}
       * @throws NullPointerException if the specified key or value is null
       */
      public V put(K key, V value) {
          return putVal(key, value, false);
      }
  
      /** Implementation for put and putIfAbsent */
      final V putVal(K key, V value, boolean onlyIfAbsent) {
          if (key == null || value == null) throw new NullPointerException();
          int hash = spread(key.hashCode());
          int binCount = 0;
          for (Node<K,V>[] tab = table;;) {
              Node<K,V> f; int n, i, fh;
              if (tab == null || (n = tab.length) == 0)
                  tab = initTable();
              else if ((f = tabAt(tab, i = (n - 1) & hash)) == null) {
                  if (casTabAt(tab, i, null,
                               new Node<K,V>(hash, key, value, null)))
                      break;                   // no lock when adding to empty bin
              }
              else if ((fh = f.hash) == MOVED)
                  tab = helpTransfer(tab, f);
              else {
                  V oldVal = null;
                  synchronized (f) {
                      if (tabAt(tab, i) == f) {
                          if (fh >= 0) {
                              binCount = 1;
                              for (Node<K,V> e = f;; ++binCount) {
                                  K ek;
                                  if (e.hash == hash &&
                                      ((ek = e.key) == key ||
                                       (ek != null && key.equals(ek)))) {
                                      oldVal = e.val;
                                      if (!onlyIfAbsent)
                                          e.val = value;
                                      break;
                                  }
                                  Node<K,V> pred = e;
                                  if ((e = e.next) == null) {
                                      pred.next = new Node<K,V>(hash, key,
                                                                value, null);
                                      break;
                                  }
                              }
                          }
                          else if (f instanceof TreeBin) {
                              Node<K,V> p;
                              binCount = 2;
                              if ((p = ((TreeBin<K,V>)f).putTreeVal(hash, key,
                                                             value)) != null) {
                                  oldVal = p.val;
                                  if (!onlyIfAbsent)
                                      p.val = value;
                              }
                          }
                          else if (f instanceof ReservationNode)
                              throw new IllegalStateException("Recursive update");
                      }
                  }
                  if (binCount != 0) {
                      if (binCount >= TREEIFY_THRESHOLD)
                          treeifyBin(tab, i);
                      if (oldVal != null)
                          return oldVal;
                      break;
                  }
              }
          }
          addCount(1L, binCount);
          return null;
      }
  
      /**
       * Copies all of the mappings from the specified map to this one.
       * These mappings replace any mappings that this map had for any of the
       * keys currently in the specified map.
       *
       * @param m mappings to be stored in this map
       */
      public void putAll(Map<? extends K, ? extends V> m) {
          tryPresize(m.size());
          for (Entry<? extends K, ? extends V> e : m.entrySet())
              putVal(e.getKey(), e.getValue(), false);
      }
  
      /**
       * Removes the key (and its corresponding value) from this map.
       * This method does nothing if the key is not in the map.
       *
       * @param  key the key that needs to be removed
       * @return the previous value associated with {@code key}, or
       *         {@code null} if there was no mapping for {@code key}
       * @throws NullPointerException if the specified key is null
       */
      public V remove(Object key) {
          return replaceNode(key, null, null);
      }
  
      /**
       * Implementation for the four public remove/replace methods:
       * Replaces node value with v, conditional upon match of cv if
       * non-null.  If resulting value is null, delete.
       */
      final V replaceNode(Object key, V value, Object cv) {
          int hash = spread(key.hashCode());
          for (Node<K,V>[] tab = table;;) {
              Node<K,V> f; int n, i, fh;
              if (tab == null || (n = tab.length) == 0 ||
                  (f = tabAt(tab, i = (n - 1) & hash)) == null)
                  break;
              else if ((fh = f.hash) == MOVED)
                  tab = helpTransfer(tab, f);
              else {
                  V oldVal = null;
                  boolean validated = false;
                  synchronized (f) {
                      if (tabAt(tab, i) == f) {
                          if (fh >= 0) {
                              validated = true;
                              for (Node<K,V> e = f, pred = null;;) {
                                  K ek;
                                  if (e.hash == hash &&
                                      ((ek = e.key) == key ||
                                       (ek != null && key.equals(ek)))) {
                                      V ev = e.val;
                                      if (cv == null || cv == ev ||
                                          (ev != null && cv.equals(ev))) {
                                          oldVal = ev;
                                          if (value != null)
                                              e.val = value;
                                          else if (pred != null)
                                              pred.next = e.next;
                                          else
                                              setTabAt(tab, i, e.next);
                                      }
                                      break;
                                  }
                                  pred = e;
                                  if ((e = e.next) == null)
                                      break;
                              }
                          }
                          else if (f instanceof TreeBin) {
                              validated = true;
                              TreeBin<K,V> t = (TreeBin<K,V>)f;
                              TreeNode<K,V> r, p;
                              if ((r = t.root) != null &&
                                  (p = r.findTreeNode(hash, key, null)) != null) {
                                  V pv = p.val;
                                  if (cv == null || cv == pv ||
                                      (pv != null && cv.equals(pv))) {
                                      oldVal = pv;
                                      if (value != null)
                                          p.val = value;
                                      else if (t.removeTreeNode(p))
                                          setTabAt(tab, i, untreeify(t.first));
                                  }
                              }
                          }
                          else if (f instanceof ReservationNode)
                              throw new IllegalStateException("Recursive update");
                      }
                  }
                  if (validated) {
                      if (oldVal != null) {
                          if (value == null)
                              addCount(-1L, -1);
                          return oldVal;
                      }
                      break;
                  }
              }
          }
          return null;
      }
  
      /**
       * Removes all of the mappings from this map.
       */
      public void clear() {
          long delta = 0L; // negative number of deletions
          int i = 0;
          Node<K,V>[] tab = table;
          while (tab != null && i < tab.length) {
              int fh;
              Node<K,V> f = tabAt(tab, i);
              if (f == null)
                  ++i;
              else if ((fh = f.hash) == MOVED) {
                  tab = helpTransfer(tab, f);
                  i = 0; // restart
              }
              else {
                  synchronized (f) {
                      if (tabAt(tab, i) == f) {
                          Node<K,V> p = (fh >= 0 ? f :
                                         (f instanceof TreeBin) ?
                                         ((TreeBin<K,V>)f).first : null);
                          while (p != null) {
                              --delta;
                              p = p.next;
                          }
                          setTabAt(tab, i++, null);
                      }
                  }
              }
          }
          if (delta != 0L)
              addCount(delta, -1);
      }
  
      /**
       * Returns a {@link Set} view of the keys contained in this map.
       * The set is backed by the map, so changes to the map are
       * reflected in the set, and vice-versa. The set supports element
       * removal, which removes the corresponding mapping from this map,
       * via the {@code Iterator.remove}, {@code Set.remove},
       * {@code removeAll}, {@code retainAll}, and {@code clear}
       * operations.  It does not support the {@code add} or
       * {@code addAll} operations.
       *
       * <p> The set returned by this method is guaranteed to an instance of
       * {@link KeySetView}.
       *
       * <p>The view's iterators and spliterators are
       * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
       *
       * <p>The view's {@code spliterator} reports {@link Spliterator#CONCURRENT},
       * {@link Spliterator#DISTINCT}, and {@link Spliterator#NONNULL}.
       *
       * @return the set view
       */
      // Android-changed: Return type for backwards compat. Was KeySetView<K,V>. http://b/28099367
      @dalvik.annotation.codegen.CovariantReturnType(returnType = KeySetView.class, presentAfter = 28)
      public Set<K> keySet() {
          KeySetView<K,V> ks;
          return (ks = keySet) != null ? ks : (keySet = new KeySetView<K,V>(this, null));
      }
  
      /**
       * Returns a {@link Collection} view of the values contained in this map.
       * The collection is backed by the map, so changes to the map are
       * reflected in the collection, and vice-versa.  The collection
       * supports element removal, which removes the corresponding
       * mapping from this map, via the {@code Iterator.remove},
       * {@code Collection.remove}, {@code removeAll},
       * {@code retainAll}, and {@code clear} operations.  It does not
       * support the {@code add} or {@code addAll} operations.
       *
       * <p>The view's iterators and spliterators are
       * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
       *
       * <p>The view's {@code spliterator} reports {@link Spliterator#CONCURRENT}
       * and {@link Spliterator#NONNULL}.
       *
       * @return the collection view
       */
      public Collection<V> values() {
          ValuesView<K,V> vs;
          return (vs = values) != null ? vs : (values = new ValuesView<K,V>(this));
      }
  
      /**
       * Returns a {@link Set} view of the mappings contained in this map.
       * The set is backed by the map, so changes to the map are
       * reflected in the set, and vice-versa.  The set supports element
       * removal, which removes the corresponding mapping from the map,
       * via the {@code Iterator.remove}, {@code Set.remove},
       * {@code removeAll}, {@code retainAll}, and {@code clear}
       * operations.
       *
       * <p>The view's iterators and spliterators are
       * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
       *
       * <p>The view's {@code spliterator} reports {@link Spliterator#CONCURRENT},
       * {@link Spliterator#DISTINCT}, and {@link Spliterator#NONNULL}.
       *
       * @return the set view
       */
      public Set<Entry<K,V>> entrySet() {
          EntrySetView<K,V> es;
          return (es = entrySet) != null ? es : (entrySet = new EntrySetView<K,V>(this));
      }
  
      /**
       * Returns the hash code value for this {@link Map}, i.e.,
       * the sum of, for each key-value pair in the map,
       * {@code key.hashCode() ^ value.hashCode()}.
       *
       * @return the hash code value for this map
       */
      public int hashCode() {
          int h = 0;
          Node<K,V>[] t;
          if ((t = table) != null) {
              Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
              for (Node<K,V> p; (p = it.advance()) != null; )
                  h += p.key.hashCode() ^ p.val.hashCode();
          }
          return h;
      }
  
      /**
       * Returns a string representation of this map.  The string
       * representation consists of a list of key-value mappings (in no
       * particular order) enclosed in braces ("{@code {}}").  Adjacent
       * mappings are separated by the characters {@code ", "} (comma
       * and space).  Each key-value mapping is rendered as the key
       * followed by an equals sign ("{@code =}") followed by the
       * associated value.
       *
       * @return a string representation of this map
       */
      public String toString() {
          Node<K,V>[] t;
          int f = (t = table) == null ? 0 : t.length;
          Traverser<K,V> it = new Traverser<K,V>(t, f, 0, f);
          StringBuilder sb = new StringBuilder();
          sb.append('{');
          Node<K,V> p;
          if ((p = it.advance()) != null) {
              for (;;) {
                  K k = p.key;
                  V v = p.val;
                  sb.append(k == this ? "(this Map)" : k);
                  sb.append('=');
                  sb.append(v == this ? "(this Map)" : v);
                  if ((p = it.advance()) == null)
                      break;
                  sb.append(',').append(' ');
              }
          }
          return sb.append('}').toString();
      }
  
      /**
       * Compares the specified object with this map for equality.
       * Returns {@code true} if the given object is a map with the same
       * mappings as this map.  This operation may return misleading
       * results if either map is concurrently modified during execution
       * of this method.
       *
       * @param o object to be compared for equality with this map
       * @return {@code true} if the specified object is equal to this map
       */
      public boolean equals(Object o) {
          if (o != this) {
              if (!(o instanceof Map))
                  return false;
              Map<?,?> m = (Map<?,?>) o;
              Node<K,V>[] t;
              int f = (t = table) == null ? 0 : t.length;
              Traverser<K,V> it = new Traverser<K,V>(t, f, 0, f);
              for (Node<K,V> p; (p = it.advance()) != null; ) {
                  V val = p.val;
                  Object v = m.get(p.key);
                  if (v == null || (v != val && !v.equals(val)))
                      return false;
              }
              for (Entry<?,?> e : m.entrySet()) {
                  Object mk, mv, v;
                  if ((mk = e.getKey()) == null ||
                      (mv = e.getValue()) == null ||
                      (v = get(mk)) == null ||
                      (mv != v && !mv.equals(v)))
                      return false;
              }
          }
          return true;
      }
  
      /**
       * Stripped-down version of helper class used in previous version,
       * declared for the sake of serialization compatibility.
       */
      static class Segment<K,V> extends ReentrantLock implements Serializable {
          private static final long serialVersionUID = 2249069246763182397L;
          final float loadFactor;
          Segment(float lf) { this.loadFactor = lf; }
      }
  
      /**
       * Saves the state of the {@code ConcurrentHashMap} instance to a
       * stream (i.e., serializes it).
       * @param s the stream
       * @throws java.io.IOException if an I/O error occurs
       * @serialData
       * the serialized fields, followed by the key (Object) and value
       * (Object) for each key-value mapping, followed by a null pair.
       * The key-value mappings are emitted in no particular order.
       */
      private void writeObject(java.io.ObjectOutputStream s)
          throws java.io.IOException {
          // For serialization compatibility
          // Emulate segment calculation from previous version of this class
          int sshift = 0;
          int ssize = 1;
          while (ssize < DEFAULT_CONCURRENCY_LEVEL) {
              ++sshift;
              ssize <<= 1;
          }
          int segmentShift = 32 - sshift;
          int segmentMask = ssize - 1;
          @SuppressWarnings("unchecked")
          Segment<K,V>[] segments = (Segment<K,V>[])
              new Segment<?,?>[DEFAULT_CONCURRENCY_LEVEL];
          for (int i = 0; i < segments.length; ++i)
              segments[i] = new Segment<K,V>(LOAD_FACTOR);
          java.io.ObjectOutputStream.PutField streamFields = s.putFields();
          streamFields.put("segments", segments);
          streamFields.put("segmentShift", segmentShift);
          streamFields.put("segmentMask", segmentMask);
          s.writeFields();
  
          Node<K,V>[] t;
          if ((t = table) != null) {
              Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
              for (Node<K,V> p; (p = it.advance()) != null; ) {
                  s.writeObject(p.key);
                  s.writeObject(p.val);
              }
          }
          s.writeObject(null);
          s.writeObject(null);
      }
  
      /**
       * Reconstitutes the instance from a stream (that is, deserializes it).
       * @param s the stream
       * @throws ClassNotFoundException if the class of a serialized object
       *         could not be found
       * @throws java.io.IOException if an I/O error occurs
       */
      private void readObject(java.io.ObjectInputStream s)
          throws java.io.IOException, ClassNotFoundException {
          /*
           * To improve performance in typical cases, we create nodes
           * while reading, then place in table once size is known.
           * However, we must also validate uniqueness and deal with
           * overpopulated bins while doing so, which requires
           * specialized versions of putVal mechanics.
           */
          sizeCtl = -1; // force exclusion for table construction
          s.defaultReadObject();
          long size = 0L;
          Node<K,V> p = null;
          for (;;) {
              @SuppressWarnings("unchecked")
              K k = (K) s.readObject();
              @SuppressWarnings("unchecked")
              V v = (V) s.readObject();
              if (k != null && v != null) {
                  p = new Node<K,V>(spread(k.hashCode()), k, v, p);
                  ++size;
              }
              else
                  break;
          }
          if (size == 0L)
              sizeCtl = 0;
          else {
              int n;
              if (size >= (long)(MAXIMUM_CAPACITY >>> 1))
                  n = MAXIMUM_CAPACITY;
              else {
                  int sz = (int)size;
                  n = tableSizeFor(sz + (sz >>> 1) + 1);
              }
              @SuppressWarnings("unchecked")
              Node<K,V>[] tab = (Node<K,V>[])new Node<?,?>[n];
              int mask = n - 1;
              long added = 0L;
              while (p != null) {
                  boolean insertAtFront;
                  Node<K,V> next = p.next, first;
                  int h = p.hash, j = h & mask;
                  if ((first = tabAt(tab, j)) == null)
                      insertAtFront = true;
                  else {
                      K k = p.key;
                      if (first.hash < 0) {
                          TreeBin<K,V> t = (TreeBin<K,V>)first;
                          if (t.putTreeVal(h, k, p.val) == null)
                              ++added;
                          insertAtFront = false;
                      }
                      else {
                          int binCount = 0;
                          insertAtFront = true;
                          Node<K,V> q; K qk;
                          for (q = first; q != null; q = q.next) {
                              if (q.hash == h &&
                                  ((qk = q.key) == k ||
                                   (qk != null && k.equals(qk)))) {
                                  insertAtFront = false;
                                  break;
                              }
                              ++binCount;
                          }
                          if (insertAtFront && binCount >= TREEIFY_THRESHOLD) {
                              insertAtFront = false;
                              ++added;
                              p.next = first;
                              TreeNode<K,V> hd = null, tl = null;
                              for (q = p; q != null; q = q.next) {
                                  TreeNode<K,V> t = new TreeNode<K,V>
                                      (q.hash, q.key, q.val, null, null);
                                  if ((t.prev = tl) == null)
                                      hd = t;
                                  else
                                      tl.next = t;
                                  tl = t;
                              }
                              setTabAt(tab, j, new TreeBin<K,V>(hd));
                          }
                      }
                  }
                  if (insertAtFront) {
                      ++added;
                      p.next = first;
                      setTabAt(tab, j, p);
                  }
                  p = next;
              }
              table = tab;
              sizeCtl = n - (n >>> 2);
              baseCount = added;
          }
      }
  
      // ConcurrentMap methods
  
      /**
       * {@inheritDoc}
       *
       * @return the previous value associated with the specified key,
       *         or {@code null} if there was no mapping for the key
       * @throws NullPointerException if the specified key or value is null
       */
      public V putIfAbsent(K key, V value) {
          return putVal(key, value, true);
      }
  
      /**
       * {@inheritDoc}
       *
       * @throws NullPointerException if the specified key is null
       */
      public boolean remove(Object key, Object value) {
          if (key == null)
              throw new NullPointerException();
          return value != null && replaceNode(key, null, value) != null;
      }
  
      /**
       * {@inheritDoc}
       *
       * @throws NullPointerException if any of the arguments are null
       */
      public boolean replace(K key, V oldValue, V newValue) {
          if (key == null || oldValue == null || newValue == null)
              throw new NullPointerException();
          return replaceNode(key, newValue, oldValue) != null;
      }
  
      /**
       * {@inheritDoc}
       *
       * @return the previous value associated with the specified key,
       *         or {@code null} if there was no mapping for the key
       * @throws NullPointerException if the specified key or value is null
       */
      public V replace(K key, V value) {
          if (key == null || value == null)
              throw new NullPointerException();
          return replaceNode(key, value, null);
      }
  
      // Overrides of JDK8+ Map extension method defaults
  
      /**
       * Returns the value to which the specified key is mapped, or the
       * given default value if this map contains no mapping for the
       * key.
       *
       * @param key the key whose associated value is to be returned
       * @param defaultValue the value to return if this map contains
       * no mapping for the given key
       * @return the mapping for the key, if present; else the default value
       * @throws NullPointerException if the specified key is null
       */
      public V getOrDefault(Object key, V defaultValue) {
          V v;
          return (v = get(key)) == null ? defaultValue : v;
      }
  
      public void forEach(BiConsumer<? super K, ? super V> action) {
          if (action == null) throw new NullPointerException();
          Node<K,V>[] t;
          if ((t = table) != null) {
              Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
              for (Node<K,V> p; (p = it.advance()) != null; ) {
                  action.accept(p.key, p.val);
              }
          }
      }
  
      public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
          if (function == null) throw new NullPointerException();
          Node<K,V>[] t;
          if ((t = table) != null) {
              Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
              for (Node<K,V> p; (p = it.advance()) != null; ) {
                  V oldValue = p.val;
                  for (K key = p.key;;) {
                      V newValue = function.apply(key, oldValue);
                      if (newValue == null)
                          throw new NullPointerException();
                      if (replaceNode(key, newValue, oldValue) != null ||
                          (oldValue = get(key)) == null)
                          break;
                  }
              }
          }
      }
  
      /**
       * Helper method for EntrySetView.removeIf.
       */
      boolean removeEntryIf(Predicate<? super Entry<K,V>> function) {
          if (function == null) throw new NullPointerException();
          Node<K,V>[] t;
          boolean removed = false;
          if ((t = table) != null) {
              Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
              for (Node<K,V> p; (p = it.advance()) != null; ) {
                  K k = p.key;
                  V v = p.val;
                  Entry<K,V> e = new SimpleImmutableEntry<>(k, v);
                  if (function.test(e) && replaceNode(k, null, v) != null)
                      removed = true;
              }
          }
          return removed;
      }
  
      /**
       * Helper method for ValuesView.removeIf.
       */
      boolean removeValueIf(Predicate<? super V> function) {
          if (function == null) throw new NullPointerException();
          Node<K,V>[] t;
          boolean removed = false;
          if ((t = table) != null) {
              Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
              for (Node<K,V> p; (p = it.advance()) != null; ) {
                  K k = p.key;
                  V v = p.val;
                  if (function.test(v) && replaceNode(k, null, v) != null)
                      removed = true;
              }
          }
          return removed;
      }
  
      /**
       * If the specified key is not already associated with a value,
       * attempts to compute its value using the given mapping function
       * and enters it into this map unless {@code null}.  The entire
       * method invocation is performed atomically, so the function is
       * applied at most once per key.  Some attempted update operations
       * on this map by other threads may be blocked while computation
       * is in progress, so the computation should be short and simple,
       * and must not attempt to update any other mappings of this map.
       *
       * @param key key with which the specified value is to be associated
       * @param mappingFunction the function to compute a value
       * @return the current (existing or computed) value associated with
       *         the specified key, or null if the computed value is null
       * @throws NullPointerException if the specified key or mappingFunction
       *         is null
       * @throws IllegalStateException if the computation detectably
       *         attempts a recursive update to this map that would
       *         otherwise never complete
       * @throws RuntimeException or Error if the mappingFunction does so,
       *         in which case the mapping is left unestablished
       */
      public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
          if (key == null || mappingFunction == null)
              throw new NullPointerException();
          int h = spread(key.hashCode());
          V val = null;
          int binCount = 0;
          for (Node<K,V>[] tab = table;;) {
              Node<K,V> f; int n, i, fh;
              if (tab == null || (n = tab.length) == 0)
                  tab = initTable();
              else if ((f = tabAt(tab, i = (n - 1) & h)) == null) {
                  Node<K,V> r = new ReservationNode<K,V>();
                  synchronized (r) {
                      if (casTabAt(tab, i, null, r)) {
                          binCount = 1;
                          Node<K,V> node = null;
                          try {
                              if ((val = mappingFunction.apply(key)) != null)
                                  node = new Node<K,V>(h, key, val, null);
                          } finally {
                              setTabAt(tab, i, node);
                          }
                      }
                  }
                  if (binCount != 0)
                      break;
              }
              else if ((fh = f.hash) == MOVED)
                  tab = helpTransfer(tab, f);
              else {
                  boolean added = false;
                  synchronized (f) {
                      if (tabAt(tab, i) == f) {
                          if (fh >= 0) {
                              binCount = 1;
                              for (Node<K,V> e = f;; ++binCount) {
                                  K ek;
                                  if (e.hash == h &&
                                      ((ek = e.key) == key ||
                                       (ek != null && key.equals(ek)))) {
                                      val = e.val;
                                      break;
                                  }
                                  Node<K,V> pred = e;
                                  if ((e = e.next) == null) {
                                      if ((val = mappingFunction.apply(key)) != null) {
                                          if (pred.next != null)
                                              throw new IllegalStateException("Recursive update");
                                          added = true;
                                          pred.next = new Node<K,V>(h, key, val, null);
                                      }
                                      break;
                                  }
                              }
                          }
                          else if (f instanceof TreeBin) {
                              binCount = 2;
                              TreeBin<K,V> t = (TreeBin<K,V>)f;
                              TreeNode<K,V> r, p;
                              if ((r = t.root) != null &&
                                  (p = r.findTreeNode(h, key, null)) != null)
                                  val = p.val;
                              else if ((val = mappingFunction.apply(key)) != null) {
                                  added = true;
                                  t.putTreeVal(h, key, val);
                              }
                          }
                          else if (f instanceof ReservationNode)
                              throw new IllegalStateException("Recursive update");
                      }
                  }
                  if (binCount != 0) {
                      if (binCount >= TREEIFY_THRESHOLD)
                          treeifyBin(tab, i);
                      if (!added)
                          return val;
                      break;
                  }
              }
          }
          if (val != null)
              addCount(1L, binCount);
          return val;
      }
  
      /**
       * If the value for the specified key is present, attempts to
       * compute a new mapping given the key and its current mapped
       * value.  The entire method invocation is performed atomically.
       * Some attempted update operations on this map by other threads
       * may be blocked while computation is in progress, so the
       * computation should be short and simple, and must not attempt to
       * update any other mappings of this map.
       *
       * @param key key with which a value may be associated
       * @param remappingFunction the function to compute a value
       * @return the new value associated with the specified key, or null if none
       * @throws NullPointerException if the specified key or remappingFunction
       *         is null
       * @throws IllegalStateException if the computation detectably
       *         attempts a recursive update to this map that would
       *         otherwise never complete
       * @throws RuntimeException or Error if the remappingFunction does so,
       *         in which case the mapping is unchanged
       */
      public V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
          if (key == null || remappingFunction == null)
              throw new NullPointerException();
          int h = spread(key.hashCode());
          V val = null;
          int delta = 0;
          int binCount = 0;
          for (Node<K,V>[] tab = table;;) {
              Node<K,V> f; int n, i, fh;
              if (tab == null || (n = tab.length) == 0)
                  tab = initTable();
              else if ((f = tabAt(tab, i = (n - 1) & h)) == null)
                  break;
              else if ((fh = f.hash) == MOVED)
                  tab = helpTransfer(tab, f);
              else {
                  synchronized (f) {
                      if (tabAt(tab, i) == f) {
                          if (fh >= 0) {
                              binCount = 1;
                              for (Node<K,V> e = f, pred = null;; ++binCount) {
                                  K ek;
                                  if (e.hash == h &&
                                      ((ek = e.key) == key ||
                                       (ek != null && key.equals(ek)))) {
                                      val = remappingFunction.apply(key, e.val);
                                      if (val != null)
                                          e.val = val;
                                      else {
                                          delta = -1;
                                          Node<K,V> en = e.next;
                                          if (pred != null)
                                              pred.next = en;
                                          else
                                              setTabAt(tab, i, en);
                                      }
                                      break;
                                  }
                                  pred = e;
                                  if ((e = e.next) == null)
                                      break;
                              }
                          }
                          else if (f instanceof TreeBin) {
                              binCount = 2;
                              TreeBin<K,V> t = (TreeBin<K,V>)f;
                              TreeNode<K,V> r, p;
                              if ((r = t.root) != null &&
                                  (p = r.findTreeNode(h, key, null)) != null) {
                                  val = remappingFunction.apply(key, p.val);
                                  if (val != null)
                                      p.val = val;
                                  else {
                                      delta = -1;
                                      if (t.removeTreeNode(p))
                                          setTabAt(tab, i, untreeify(t.first));
                                  }
                              }
                          }
                          else if (f instanceof ReservationNode)
                              throw new IllegalStateException("Recursive update");
                      }
                  }
                  if (binCount != 0)
                      break;
              }
          }
          if (delta != 0)
              addCount((long)delta, binCount);
          return val;
      }
  
      /**
       * Attempts to compute a mapping for the specified key and its
       * current mapped value (or {@code null} if there is no current
       * mapping). The entire method invocation is performed atomically.
       * Some attempted update operations on this map by other threads
       * may be blocked while computation is in progress, so the
       * computation should be short and simple, and must not attempt to
       * update any other mappings of this Map.
       *
       * @param key key with which the specified value is to be associated
       * @param remappingFunction the function to compute a value
       * @return the new value associated with the specified key, or null if none
       * @throws NullPointerException if the specified key or remappingFunction
       *         is null
       * @throws IllegalStateException if the computation detectably
       *         attempts a recursive update to this map that would
       *         otherwise never complete
       * @throws RuntimeException or Error if the remappingFunction does so,
       *         in which case the mapping is unchanged
       */
      public V compute(K key,
                       BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
          if (key == null || remappingFunction == null)
              throw new NullPointerException();
          int h = spread(key.hashCode());
          V val = null;
          int delta = 0;
          int binCount = 0;
          for (Node<K,V>[] tab = table;;) {
              Node<K,V> f; int n, i, fh;
              if (tab == null || (n = tab.length) == 0)
                  tab = initTable();
              else if ((f = tabAt(tab, i = (n - 1) & h)) == null) {
                  Node<K,V> r = new ReservationNode<K,V>();
                  synchronized (r) {
                      if (casTabAt(tab, i, null, r)) {
                          binCount = 1;
                          Node<K,V> node = null;
                          try {
                              if ((val = remappingFunction.apply(key, null)) != null) {
                                  delta = 1;
                                  node = new Node<K,V>(h, key, val, null);
                              }
                          } finally {
                              setTabAt(tab, i, node);
                          }
                      }
                  }
                  if (binCount != 0)
                      break;
              }
              else if ((fh = f.hash) == MOVED)
                  tab = helpTransfer(tab, f);
              else {
                  synchronized (f) {
                      if (tabAt(tab, i) == f) {
                          if (fh >= 0) {
                              binCount = 1;
                              for (Node<K,V> e = f, pred = null;; ++binCount) {
                                  K ek;
                                  if (e.hash == h &&
                                      ((ek = e.key) == key ||
                                       (ek != null && key.equals(ek)))) {
                                      val = remappingFunction.apply(key, e.val);
                                      if (val != null)
                                          e.val = val;
                                      else {
                                          delta = -1;
                                          Node<K,V> en = e.next;
                                          if (pred != null)
                                              pred.next = en;
                                          else
                                              setTabAt(tab, i, en);
                                      }
                                      break;
                                  }
                                  pred = e;
                                  if ((e = e.next) == null) {
                                      val = remappingFunction.apply(key, null);
                                      if (val != null) {
                                          if (pred.next != null)
                                              throw new IllegalStateException("Recursive update");
                                          delta = 1;
                                          pred.next =
                                              new Node<K,V>(h, key, val, null);
                                      }
                                      break;
                                  }
                              }
                          }
                          else if (f instanceof TreeBin) {
                              binCount = 1;
                              TreeBin<K,V> t = (TreeBin<K,V>)f;
                              TreeNode<K,V> r, p;
                              if ((r = t.root) != null)
                                  p = r.findTreeNode(h, key, null);
                              else
                                  p = null;
                              V pv = (p == null) ? null : p.val;
                              val = remappingFunction.apply(key, pv);
                              if (val != null) {
                                  if (p != null)
                                      p.val = val;
                                  else {
                                      delta = 1;
                                      t.putTreeVal(h, key, val);
                                  }
                              }
                              else if (p != null) {
                                  delta = -1;
                                  if (t.removeTreeNode(p))
                                      setTabAt(tab, i, untreeify(t.first));
                              }
                          }
                          else if (f instanceof ReservationNode)
                              throw new IllegalStateException("Recursive update");
                      }
                  }
                  if (binCount != 0) {
                      if (binCount >= TREEIFY_THRESHOLD)
                          treeifyBin(tab, i);
                      break;
                  }
              }
          }
          if (delta != 0)
              addCount((long)delta, binCount);
          return val;
      }
  
      /**
       * If the specified key is not already associated with a
       * (non-null) value, associates it with the given value.
       * Otherwise, replaces the value with the results of the given
       * remapping function, or removes if {@code null}. The entire
       * method invocation is performed atomically.  Some attempted
       * update operations on this map by other threads may be blocked
       * while computation is in progress, so the computation should be
       * short and simple, and must not attempt to update any other
       * mappings of this Map.
       *
       * @param key key with which the specified value is to be associated
       * @param value the value to use if absent
       * @param remappingFunction the function to recompute a value if present
       * @return the new value associated with the specified key, or null if none
       * @throws NullPointerException if the specified key or the
       *         remappingFunction is null
       * @throws RuntimeException or Error if the remappingFunction does so,
       *         in which case the mapping is unchanged
       */
      public V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
          if (key == null || value == null || remappingFunction == null)
              throw new NullPointerException();
          int h = spread(key.hashCode());
          V val = null;
          int delta = 0;
          int binCount = 0;
          for (Node<K,V>[] tab = table;;) {
              Node<K,V> f; int n, i, fh;
              if (tab == null || (n = tab.length) == 0)
                  tab = initTable();
              else if ((f = tabAt(tab, i = (n - 1) & h)) == null) {
                  if (casTabAt(tab, i, null, new Node<K,V>(h, key, value, null))) {
                      delta = 1;
                      val = value;
                      break;
                  }
              }
              else if ((fh = f.hash) == MOVED)
                  tab = helpTransfer(tab, f);
              else {
                  synchronized (f) {
                      if (tabAt(tab, i) == f) {
                          if (fh >= 0) {
                              binCount = 1;
                              for (Node<K,V> e = f, pred = null;; ++binCount) {
                                  K ek;
                                  if (e.hash == h &&
                                      ((ek = e.key) == key ||
                                       (ek != null && key.equals(ek)))) {
                                      val = remappingFunction.apply(e.val, value);
                                      if (val != null)
                                          e.val = val;
                                      else {
                                          delta = -1;
                                          Node<K,V> en = e.next;
                                          if (pred != null)
                                              pred.next = en;
                                          else
                                              setTabAt(tab, i, en);
                                      }
                                      break;
                                  }
                                  pred = e;
                                  if ((e = e.next) == null) {
                                      delta = 1;
                                      val = value;
                                      pred.next =
                                          new Node<K,V>(h, key, val, null);
                                      break;
                                  }
                              }
                          }
                          else if (f instanceof TreeBin) {
                              binCount = 2;
                              TreeBin<K,V> t = (TreeBin<K,V>)f;
                              TreeNode<K,V> r = t.root;
                              TreeNode<K,V> p = (r == null) ? null :
                                  r.findTreeNode(h, key, null);
                              val = (p == null) ? value :
                                  remappingFunction.apply(p.val, value);
                              if (val != null) {
                                  if (p != null)
                                      p.val = val;
                                  else {
                                      delta = 1;
                                      t.putTreeVal(h, key, val);
                                  }
                              }
                              else if (p != null) {
                                  delta = -1;
                                  if (t.removeTreeNode(p))
                                      setTabAt(tab, i, untreeify(t.first));
                              }
                          }
                          else if (f instanceof ReservationNode)
                              throw new IllegalStateException("Recursive update");
                      }
                  }
                  if (binCount != 0) {
                      if (binCount >= TREEIFY_THRESHOLD)
                          treeifyBin(tab, i);
                      break;
                  }
              }
          }
          if (delta != 0)
              addCount((long)delta, binCount);
          return val;
      }
  
      // Hashtable legacy methods
  
      /**
       * Tests if some key maps into the specified value in this table.
       *
       * <p>Note that this method is identical in functionality to
       * {@link #containsValue(Object)}, and exists solely to ensure
       * full compatibility with class {@link Hashtable},
       * which supported this method prior to introduction of the
       * Java Collections Framework.
       *
       * @param  value a value to search for
       * @return {@code true} if and only if some key maps to the
       *         {@code value} argument in this table as
       *         determined by the {@code equals} method;
       *         {@code false} otherwise
       * @throws NullPointerException if the specified value is null
       */
      public boolean contains(Object value) {
          return containsValue(value);
      }
  
      /**
       * Returns an enumeration of the keys in this table.
       *
       * @return an enumeration of the keys in this table
       * @see #keySet()
       */
      public Enumeration<K> keys() {
          Node<K,V>[] t;
          int f = (t = table) == null ? 0 : t.length;
          return new KeyIterator<K,V>(t, f, 0, f, this);
      }
  
      /**
       * Returns an enumeration of the values in this table.
       *
       * @return an enumeration of the values in this table
       * @see #values()
       */
      public Enumeration<V> elements() {
          Node<K,V>[] t;
          int f = (t = table) == null ? 0 : t.length;
          return new ValueIterator<K,V>(t, f, 0, f, this);
      }
  
      // ConcurrentHashMap-only methods
  
      /**
       * Returns the number of mappings. This method should be used
       * instead of {@link #size} because a ConcurrentHashMap may
       * contain more mappings than can be represented as an int. The
       * value returned is an estimate; the actual count may differ if
       * there are concurrent insertions or removals.
       *
       * @return the number of mappings
       * @since 1.8
       */
      public long mappingCount() {
          long n = sumCount();
          return (n < 0L) ? 0L : n; // ignore transient negative values
      }
  
      /**
       * Creates a new {@link Set} backed by a ConcurrentHashMap
       * from the given type to {@code Boolean.TRUE}.
       *
       * @param <K> the element type of the returned set
       * @return the new set
       * @since 1.8
       */
      public static <K> KeySetView<K,Boolean> newKeySet() {
          return new KeySetView<K,Boolean>
              (new ConcurrentHashMap<K,Boolean>(), Boolean.TRUE);
      }
  
      /**
       * Creates a new {@link Set} backed by a ConcurrentHashMap
       * from the given type to {@code Boolean.TRUE}.
       *
       * @param initialCapacity The implementation performs internal
       * sizing to accommodate this many elements.
       * @param <K> the element type of the returned set
       * @return the new set
       * @throws IllegalArgumentException if the initial capacity of
       * elements is negative
       * @since 1.8
       */
      public static <K> KeySetView<K,Boolean> newKeySet(int initialCapacity) {
          return new KeySetView<K,Boolean>
              (new ConcurrentHashMap<K,Boolean>(initialCapacity), Boolean.TRUE);
      }
  
      /**
       * Returns a {@link Set} view of the keys in this map, using the
       * given common mapped value for any additions (i.e., {@link
       * Collection#add} and {@link Collection#addAll(Collection)}).
       * This is of course only appropriate if it is acceptable to use
       * the same value for all additions from this view.
       *
       * @param mappedValue the mapped value to use for any additions
       * @return the set view
       * @throws NullPointerException if the mappedValue is null
       */
      public KeySetView<K,V> keySet(V mappedValue) {
          if (mappedValue == null)
              throw new NullPointerException();
          return new KeySetView<K,V>(this, mappedValue);
      }
  
      /* ---------------- Special Nodes -------------- */
  
      /**
       * A node inserted at head of bins during transfer operations.
       */
      static final class ForwardingNode<K,V> extends Node<K,V> {
          final Node<K,V>[] nextTable;
          ForwardingNode(Node<K,V>[] tab) {
              super(MOVED, null, null, null);
              this.nextTable = tab;
          }
  
          Node<K,V> find(int h, Object k) {
              // loop to avoid arbitrarily deep recursion on forwarding nodes
              outer: for (Node<K,V>[] tab = nextTable;;) {
                  Node<K,V> e; int n;
                  if (k == null || tab == null || (n = tab.length) == 0 ||
                      (e = tabAt(tab, (n - 1) & h)) == null)
                      return null;
                  for (;;) {
                      int eh; K ek;
                      if ((eh = e.hash) == h &&
                          ((ek = e.key) == k || (ek != null && k.equals(ek))))
                          return e;
                      if (eh < 0) {
                          if (e instanceof ForwardingNode) {
                              tab = ((ForwardingNode<K,V>)e).nextTable;
                              continue outer;
                          }
                          else
                              return e.find(h, k);
                      }
                      if ((e = e.next) == null)
                          return null;
                  }
              }
          }
      }
  
      /**
       * A place-holder node used in computeIfAbsent and compute.
       */
      static final class ReservationNode<K,V> extends Node<K,V> {
          ReservationNode() {
              super(RESERVED, null, null, null);
          }
  
          Node<K,V> find(int h, Object k) {
              return null;
          }
      }
  
      /* ---------------- Table Initialization and Resizing -------------- */
  
      /**
       * Returns the stamp bits for resizing a table of size n.
       * Must be negative when shifted left by RESIZE_STAMP_SHIFT.
       */
      static final int resizeStamp(int n) {
          return Integer.numberOfLeadingZeros(n) | (1 << (RESIZE_STAMP_BITS - 1));
      }
  
      /**
       * Initializes table, using the size recorded in sizeCtl.
       */
      private final Node<K,V>[] initTable() {
          Node<K,V>[] tab; int sc;
          while ((tab = table) == null || tab.length == 0) {
              if ((sc = sizeCtl) < 0)
                  Thread.yield(); // lost initialization race; just spin
              else if (U.compareAndSwapInt(this, SIZECTL, sc, -1)) {
                  try {
                      if ((tab = table) == null || tab.length == 0) {
                          int n = (sc > 0) ? sc : DEFAULT_CAPACITY;
                          @SuppressWarnings("unchecked")
                          Node<K,V>[] nt = (Node<K,V>[])new Node<?,?>[n];
                          table = tab = nt;
                          sc = n - (n >>> 2);
                      }
                  } finally {
                      sizeCtl = sc;
                  }
                  break;
              }
          }
          return tab;
      }
  
      /**
       * Adds to count, and if table is too small and not already
       * resizing, initiates transfer. If already resizing, helps
       * perform transfer if work is available.  Rechecks occupancy
       * after a transfer to see if another resize is already needed
       * because resizings are lagging additions.
       *
       * @param x the count to add
       * @param check if <0, don't check resize, if <= 1 only check if uncontended
       */
      private final void addCount(long x, int check) {
          CounterCell[] as; long b, s;
          if ((as = counterCells) != null ||
              !U.compareAndSwapLong(this, BASECOUNT, b = baseCount, s = b + x)) {
              CounterCell a; long v; int m;
              boolean uncontended = true;
              if (as == null || (m = as.length - 1) < 0 ||
                  (a = as[ThreadLocalRandom.getProbe() & m]) == null ||
                  !(uncontended =
                    U.compareAndSwapLong(a, CELLVALUE, v = a.value, v + x))) {
                  fullAddCount(x, uncontended);
                  return;
              }
              if (check <= 1)
                  return;
              s = sumCount();
          }
          if (check >= 0) {
              Node<K,V>[] tab, nt; int n, sc;
              while (s >= (long)(sc = sizeCtl) && (tab = table) != null &&
                     (n = tab.length) < MAXIMUM_CAPACITY) {
                  int rs = resizeStamp(n);
                  if (sc < 0) {
                      if ((sc >>> RESIZE_STAMP_SHIFT) != rs || sc == rs + 1 ||
                          sc == rs + MAX_RESIZERS || (nt = nextTable) == null ||
                          transferIndex <= 0)
                          break;
                      if (U.compareAndSwapInt(this, SIZECTL, sc, sc + 1))
                          transfer(tab, nt);
                  }
                  else if (U.compareAndSwapInt(this, SIZECTL, sc,
                                               (rs << RESIZE_STAMP_SHIFT) + 2))
                      transfer(tab, null);
                  s = sumCount();
              }
          }
      }
  
      /**
       * Helps transfer if a resize is in progress.
       */
      final Node<K,V>[] helpTransfer(Node<K,V>[] tab, Node<K,V> f) {
          Node<K,V>[] nextTab; int sc;
          if (tab != null && (f instanceof ForwardingNode) &&
              (nextTab = ((ForwardingNode<K,V>)f).nextTable) != null) {
              int rs = resizeStamp(tab.length);
              while (nextTab == nextTable && table == tab &&
                     (sc = sizeCtl) < 0) {
                  if ((sc >>> RESIZE_STAMP_SHIFT) != rs || sc == rs + 1 ||
                      sc == rs + MAX_RESIZERS || transferIndex <= 0)
                      break;
                  if (U.compareAndSwapInt(this, SIZECTL, sc, sc + 1)) {
                      transfer(tab, nextTab);
                      break;
                  }
              }
              return nextTab;
          }
          return table;
      }
  
      /**
       * Tries to presize table to accommodate the given number of elements.
       *
       * @param size number of elements (doesn't need to be perfectly accurate)
       */
      private final void tryPresize(int size) {
          int c = (size >= (MAXIMUM_CAPACITY >>> 1)) ? MAXIMUM_CAPACITY :
              tableSizeFor(size + (size >>> 1) + 1);
          int sc;
          while ((sc = sizeCtl) >= 0) {
              Node<K,V>[] tab = table; int n;
              if (tab == null || (n = tab.length) == 0) {
                  n = (sc > c) ? sc : c;
                  if (U.compareAndSwapInt(this, SIZECTL, sc, -1)) {
                      try {
                          if (table == tab) {
                              @SuppressWarnings("unchecked")
                              Node<K,V>[] nt = (Node<K,V>[])new Node<?,?>[n];
                              table = nt;
                              sc = n - (n >>> 2);
                          }
                      } finally {
                          sizeCtl = sc;
                      }
                  }
              }
              else if (c <= sc || n >= MAXIMUM_CAPACITY)
                  break;
              else if (tab == table) {
                  int rs = resizeStamp(n);
                  if (U.compareAndSwapInt(this, SIZECTL, sc,
                                          (rs << RESIZE_STAMP_SHIFT) + 2))
                      transfer(tab, null);
              }
          }
      }
  
      /**
       * Moves and/or copies the nodes in each bin to new table. See
       * above for explanation.
       */
      private final void transfer(Node<K,V>[] tab, Node<K,V>[] nextTab) {
          int n = tab.length, stride;
          if ((stride = (NCPU > 1) ? (n >>> 3) / NCPU : n) < MIN_TRANSFER_STRIDE)
              stride = MIN_TRANSFER_STRIDE; // subdivide range
          if (nextTab == null) {            // initiating
              try {
                  @SuppressWarnings("unchecked")
                  Node<K,V>[] nt = (Node<K,V>[])new Node<?,?>[n << 1];
                  nextTab = nt;
              } catch (Throwable ex) {      // try to cope with OOME
                  sizeCtl = Integer.MAX_VALUE;
                  return;
              }
              nextTable = nextTab;
              transferIndex = n;
          }
          int nextn = nextTab.length;
          ForwardingNode<K,V> fwd = new ForwardingNode<K,V>(nextTab);
          boolean advance = true;
          boolean finishing = false; // to ensure sweep before committing nextTab
          for (int i = 0, bound = 0;;) {
              Node<K,V> f; int fh;
              while (advance) {
                  int nextIndex, nextBound;
                  if (--i >= bound || finishing)
                      advance = false;
                  else if ((nextIndex = transferIndex) <= 0) {
                      i = -1;
                      advance = false;
                  }
                  else if (U.compareAndSwapInt
                           (this, TRANSFERINDEX, nextIndex,
                            nextBound = (nextIndex > stride ?
                                         nextIndex - stride : 0))) {
                      bound = nextBound;
                      i = nextIndex - 1;
                      advance = false;
                  }
              }
              if (i < 0 || i >= n || i + n >= nextn) {
                  int sc;
                  if (finishing) {
                      nextTable = null;
                      table = nextTab;
                      sizeCtl = (n << 1) - (n >>> 1);
                      return;
                  }
                  if (U.compareAndSwapInt(this, SIZECTL, sc = sizeCtl, sc - 1)) {
                      if ((sc - 2) != resizeStamp(n) << RESIZE_STAMP_SHIFT)
                          return;
                      finishing = advance = true;
                      i = n; // recheck before commit
                  }
              }
              else if ((f = tabAt(tab, i)) == null)
                  advance = casTabAt(tab, i, null, fwd);
              else if ((fh = f.hash) == MOVED)
                  advance = true; // already processed
              else {
                  synchronized (f) {
                      if (tabAt(tab, i) == f) {
                          Node<K,V> ln, hn;
                          if (fh >= 0) {
                              int runBit = fh & n;
                              Node<K,V> lastRun = f;
                              for (Node<K,V> p = f.next; p != null; p = p.next) {
                                  int b = p.hash & n;
                                  if (b != runBit) {
                                      runBit = b;
                                      lastRun = p;
                                  }
                              }
                              if (runBit == 0) {
                                  ln = lastRun;
                                  hn = null;
                              }
                              else {
                                  hn = lastRun;
                                  ln = null;
                              }
                              for (Node<K,V> p = f; p != lastRun; p = p.next) {
                                  int ph = p.hash; K pk = p.key; V pv = p.val;
                                  if ((ph & n) == 0)
                                      ln = new Node<K,V>(ph, pk, pv, ln);
                                  else
                                      hn = new Node<K,V>(ph, pk, pv, hn);
                              }
                              setTabAt(nextTab, i, ln);
                              setTabAt(nextTab, i + n, hn);
                              setTabAt(tab, i, fwd);
                              advance = true;
                          }
                          else if (f instanceof TreeBin) {
                              TreeBin<K,V> t = (TreeBin<K,V>)f;
                              TreeNode<K,V> lo = null, loTail = null;
                              TreeNode<K,V> hi = null, hiTail = null;
                              int lc = 0, hc = 0;
                              for (Node<K,V> e = t.first; e != null; e = e.next) {
                                  int h = e.hash;
                                  TreeNode<K,V> p = new TreeNode<K,V>
                                      (h, e.key, e.val, null, null);
                                  if ((h & n) == 0) {
                                      if ((p.prev = loTail) == null)
                                          lo = p;
                                      else
                                          loTail.next = p;
                                      loTail = p;
                                      ++lc;
                                  }
                                  else {
                                      if ((p.prev = hiTail) == null)
                                          hi = p;
                                      else
                                          hiTail.next = p;
                                      hiTail = p;
                                      ++hc;
                                  }
                              }
                              ln = (lc <= UNTREEIFY_THRESHOLD) ? untreeify(lo) :
                                  (hc != 0) ? new TreeBin<K,V>(lo) : t;
                              hn = (hc <= UNTREEIFY_THRESHOLD) ? untreeify(hi) :
                                  (lc != 0) ? new TreeBin<K,V>(hi) : t;
                              setTabAt(nextTab, i, ln);
                              setTabAt(nextTab, i + n, hn);
                              setTabAt(tab, i, fwd);
                              advance = true;
                          }
                      }
                  }
              }
          }
      }
  
      /* ---------------- Counter support -------------- */
  
      /**
       * A padded cell for distributing counts.  Adapted from LongAdder
       * and Striped64.  See their internal docs for explanation.
       */
      // Android-removed: @Contended, this hint is not used by the Android runtime.
      //@jdk.internal.vm.annotation.Contended
      static final class CounterCell {
          volatile long value;
          CounterCell(long x) { value = x; }
      }
  
      final long sumCount() {
          CounterCell[] as = counterCells; CounterCell a;
          long sum = baseCount;
          if (as != null) {
              for (int i = 0; i < as.length; ++i) {
                  if ((a = as[i]) != null)
                      sum += a.value;
              }
          }
          return sum;
      }
  
      // See LongAdder version for explanation
      private final void fullAddCount(long x, boolean wasUncontended) {
          int h;
          if ((h = ThreadLocalRandom.getProbe()) == 0) {
              ThreadLocalRandom.localInit();      // force initialization
              h = ThreadLocalRandom.getProbe();
              wasUncontended = true;
          }
          boolean collide = false;                // True if last slot nonempty
          for (;;) {
              CounterCell[] as; CounterCell a; int n; long v;
              if ((as = counterCells) != null && (n = as.length) > 0) {
                  if ((a = as[(n - 1) & h]) == null) {
                      if (cellsBusy == 0) {            // Try to attach new Cell
                          CounterCell r = new CounterCell(x); // Optimistic create
                          if (cellsBusy == 0 &&
                              U.compareAndSwapInt(this, CELLSBUSY, 0, 1)) {
                              boolean created = false;
                              try {               // Recheck under lock
                                  CounterCell[] rs; int m, j;
                                  if ((rs = counterCells) != null &&
                                      (m = rs.length) > 0 &&
                                      rs[j = (m - 1) & h] == null) {
                                      rs[j] = r;
                                      created = true;
                                  }
                              } finally {
                                  cellsBusy = 0;
                              }
                              if (created)
                                  break;
                              continue;           // Slot is now non-empty
                          }
                      }
                      collide = false;
                  }
                  else if (!wasUncontended)       // CAS already known to fail
                      wasUncontended = true;      // Continue after rehash
                  else if (U.compareAndSwapLong(a, CELLVALUE, v = a.value, v + x))
                      break;
                  else if (counterCells != as || n >= NCPU)
                      collide = false;            // At max size or stale
                  else if (!collide)
                      collide = true;
                  else if (cellsBusy == 0 &&
                           U.compareAndSwapInt(this, CELLSBUSY, 0, 1)) {
                      try {
                          if (counterCells == as) {// Expand table unless stale
                              CounterCell[] rs = new CounterCell[n << 1];
                              for (int i = 0; i < n; ++i)
                                  rs[i] = as[i];
                              counterCells = rs;
                          }
                      } finally {
                          cellsBusy = 0;
                      }
                      collide = false;
                      continue;                   // Retry with expanded table
                  }
                  h = ThreadLocalRandom.advanceProbe(h);
              }
              else if (cellsBusy == 0 && counterCells == as &&
                       U.compareAndSwapInt(this, CELLSBUSY, 0, 1)) {
                  boolean init = false;
                  try {                           // Initialize table
                      if (counterCells == as) {
                          CounterCell[] rs = new CounterCell[2];
                          rs[h & 1] = new CounterCell(x);
                          counterCells = rs;
                          init = true;
                      }
                  } finally {
                      cellsBusy = 0;
                  }
                  if (init)
                      break;
              }
              else if (U.compareAndSwapLong(this, BASECOUNT, v = baseCount, v + x))
                  break;                          // Fall back on using base
          }
      }
  
      /* ---------------- Conversion from/to TreeBins -------------- */
  
      /**
       * Replaces all linked nodes in bin at given index unless table is
       * too small, in which case resizes instead.
       */
      private final void treeifyBin(Node<K,V>[] tab, int index) {
          Node<K,V> b; int n;
          if (tab != null) {
              if ((n = tab.length) < MIN_TREEIFY_CAPACITY)
                  tryPresize(n << 1);
              else if ((b = tabAt(tab, index)) != null && b.hash >= 0) {
                  synchronized (b) {
                      if (tabAt(tab, index) == b) {
                          TreeNode<K,V> hd = null, tl = null;
                          for (Node<K,V> e = b; e != null; e = e.next) {
                              TreeNode<K,V> p =
                                  new TreeNode<K,V>(e.hash, e.key, e.val,
                                                    null, null);
                              if ((p.prev = tl) == null)
                                  hd = p;
                              else
                                  tl.next = p;
                              tl = p;
                          }
                          setTabAt(tab, index, new TreeBin<K,V>(hd));
                      }
                  }
              }
          }
      }
  
      /**
       * Returns a list on non-TreeNodes replacing those in given list.
       */
      static <K,V> Node<K,V> untreeify(Node<K,V> b) {
          Node<K,V> hd = null, tl = null;
          for (Node<K,V> q = b; q != null; q = q.next) {
              Node<K,V> p = new Node<K,V>(q.hash, q.key, q.val, null);
              if (tl == null)
                  hd = p;
              else
                  tl.next = p;
              tl = p;
          }
          return hd;
      }
  
      /* ---------------- TreeNodes -------------- */
  
      /**
       * Nodes for use in TreeBins.
       */
      static final class TreeNode<K,V> extends Node<K,V> {
          TreeNode<K,V> parent;  // red-black tree links
          TreeNode<K,V> left;
          TreeNode<K,V> right;
          TreeNode<K,V> prev;    // needed to unlink next upon deletion
          boolean red;
  
          TreeNode(int hash, K key, V val, Node<K,V> next,
                   TreeNode<K,V> parent) {
              super(hash, key, val, next);
              this.parent = parent;
          }
  
          Node<K,V> find(int h, Object k) {
              return findTreeNode(h, k, null);
          }
  
          /**
           * Returns the TreeNode (or null if not found) for the given key
           * starting at given root.
           */
          final TreeNode<K,V> findTreeNode(int h, Object k, Class<?> kc) {
              if (k != null) {
                  TreeNode<K,V> p = this;
                  do {
                      int ph, dir; K pk; TreeNode<K,V> q;
                      TreeNode<K,V> pl = p.left, pr = p.right;
                      if ((ph = p.hash) > h)
                          p = pl;
                      else if (ph < h)
                          p = pr;
                      else if ((pk = p.key) == k || (pk != null && k.equals(pk)))
                          return p;
                      else if (pl == null)
                          p = pr;
                      else if (pr == null)
                          p = pl;
                      else if ((kc != null ||
                                (kc = comparableClassFor(k)) != null) &&
                               (dir = compareComparables(kc, k, pk)) != 0)
                          p = (dir < 0) ? pl : pr;
                      else if ((q = pr.findTreeNode(h, k, kc)) != null)
                          return q;
                      else
                          p = pl;
                  } while (p != null);
              }
              return null;
          }
      }
  
      /* ---------------- TreeBins -------------- */
  
      /**
       * TreeNodes used at the heads of bins. TreeBins do not hold user
       * keys or values, but instead point to list of TreeNodes and
       * their root. They also maintain a parasitic read-write lock
       * forcing writers (who hold bin lock) to wait for readers (who do
       * not) to complete before tree restructuring operations.
       */
      static final class TreeBin<K,V> extends Node<K,V> {
          TreeNode<K,V> root;
          volatile TreeNode<K,V> first;
          volatile Thread waiter;
          volatile int lockState;
          // values for lockState
          static final int WRITER = 1; // set while holding write lock
          static final int WAITER = 2; // set when waiting for write lock
          static final int READER = 4; // increment value for setting read lock
  
          /**
           * Tie-breaking utility for ordering insertions when equal
           * hashCodes and non-comparable. We don't require a total
           * order, just a consistent insertion rule to maintain
           * equivalence across rebalancings. Tie-breaking further than
           * necessary simplifies testing a bit.
           */
          static int tieBreakOrder(Object a, Object b) {
              int d;
              if (a == null || b == null ||
                  (d = a.getClass().getName().
                   compareTo(b.getClass().getName())) == 0)
                  d = (System.identityHashCode(a) <= System.identityHashCode(b) ?
                       -1 : 1);
              return d;
          }
  
          /**
           * Creates bin with initial set of nodes headed by b.
           */
          TreeBin(TreeNode<K,V> b) {
              super(TREEBIN, null, null, null);
              this.first = b;
              TreeNode<K,V> r = null;
              for (TreeNode<K,V> x = b, next; x != null; x = next) {
                  next = (TreeNode<K,V>)x.next;
                  x.left = x.right = null;
                  if (r == null) {
                      x.parent = null;
                      x.red = false;
                      r = x;
                  }
                  else {
                      K k = x.key;
                      int h = x.hash;
                      Class<?> kc = null;
                      for (TreeNode<K,V> p = r;;) {
                          int dir, ph;
                          K pk = p.key;
                          if ((ph = p.hash) > h)
                              dir = -1;
                          else if (ph < h)
                              dir = 1;
                          else if ((kc == null &&
                                    (kc = comparableClassFor(k)) == null) ||
                                   (dir = compareComparables(kc, k, pk)) == 0)
                              dir = tieBreakOrder(k, pk);
                          TreeNode<K,V> xp = p;
                          if ((p = (dir <= 0) ? p.left : p.right) == null) {
                              x.parent = xp;
                              if (dir <= 0)
                                  xp.left = x;
                              else
                                  xp.right = x;
                              r = balanceInsertion(r, x);
                              break;
                          }
                      }
                  }
              }
              this.root = r;
              assert checkInvariants(root);
          }
  
          /**
           * Acquires write lock for tree restructuring.
           */
          private final void lockRoot() {
              if (!U.compareAndSwapInt(this, LOCKSTATE, 0, WRITER))
                  contendedLock(); // offload to separate method
          }
  
          /**
           * Releases write lock for tree restructuring.
           */
          private final void unlockRoot() {
              lockState = 0;
          }
  
          /**
           * Possibly blocks awaiting root lock.
           */
          private final void contendedLock() {
              boolean waiting = false;
              for (int s;;) {
                  if (((s = lockState) & ~WAITER) == 0) {
                      if (U.compareAndSwapInt(this, LOCKSTATE, s, WRITER)) {
                          if (waiting)
                              waiter = null;
                          return;
                      }
                  }
                  else if ((s & WAITER) == 0) {
                      if (U.compareAndSwapInt(this, LOCKSTATE, s, s | WAITER)) {
                          waiting = true;
                          waiter = Thread.currentThread();
                      }
                  }
                  else if (waiting)
                      LockSupport.park(this);
              }
          }
  
          /**
           * Returns matching node or null if none. Tries to search
           * using tree comparisons from root, but continues linear
           * search when lock not available.
           */
          final Node<K,V> find(int h, Object k) {
              if (k != null) {
                  for (Node<K,V> e = first; e != null; ) {
                      int s; K ek;
                      if (((s = lockState) & (WAITER|WRITER)) != 0) {
                          if (e.hash == h &&
                              ((ek = e.key) == k || (ek != null && k.equals(ek))))
                              return e;
                          e = e.next;
                      }
                      else if (U.compareAndSwapInt(this, LOCKSTATE, s,
                                                   s + READER)) {
                          TreeNode<K,V> r, p;
                          try {
                              p = ((r = root) == null ? null :
                                   r.findTreeNode(h, k, null));
                          } finally {
                              Thread w;
                              if (U.getAndAddInt(this, LOCKSTATE, -READER) ==
                                  (READER|WAITER) && (w = waiter) != null)
                                  LockSupport.unpark(w);
                          }
                          return p;
                      }
                  }
              }
              return null;
          }
  
          /**
           * Finds or adds a node.
           * @return null if added
           */
          final TreeNode<K,V> putTreeVal(int h, K k, V v) {
              Class<?> kc = null;
              boolean searched = false;
              for (TreeNode<K,V> p = root;;) {
                  int dir, ph; K pk;
                  if (p == null) {
                      first = root = new TreeNode<K,V>(h, k, v, null, null);
                      break;
                  }
                  else if ((ph = p.hash) > h)
                      dir = -1;
                  else if (ph < h)
                      dir = 1;
                  else if ((pk = p.key) == k || (pk != null && k.equals(pk)))
                      return p;
                  else if ((kc == null &&
                            (kc = comparableClassFor(k)) == null) ||
                           (dir = compareComparables(kc, k, pk)) == 0) {
                      if (!searched) {
                          TreeNode<K,V> q, ch;
                          searched = true;
                          if (((ch = p.left) != null &&
                               (q = ch.findTreeNode(h, k, kc)) != null) ||
                              ((ch = p.right) != null &&
                               (q = ch.findTreeNode(h, k, kc)) != null))
                              return q;
                      }
                      dir = tieBreakOrder(k, pk);
                  }
  
                  TreeNode<K,V> xp = p;
                  if ((p = (dir <= 0) ? p.left : p.right) == null) {
                      TreeNode<K,V> x, f = first;
                      first = x = new TreeNode<K,V>(h, k, v, f, xp);
                      if (f != null)
                          f.prev = x;
                      if (dir <= 0)
                          xp.left = x;
                      else
                          xp.right = x;
                      if (!xp.red)
                          x.red = true;
                      else {
                          lockRoot();
                          try {
                              root = balanceInsertion(root, x);
                          } finally {
                              unlockRoot();
                          }
                      }
                      break;
                  }
              }
              assert checkInvariants(root);
              return null;
          }
  
          /**
           * Removes the given node, that must be present before this
           * call.  This is messier than typical red-black deletion code
           * because we cannot swap the contents of an interior node
           * with a leaf successor that is pinned by "next" pointers
           * that are accessible independently of lock. So instead we
           * swap the tree linkages.
           *
           * @return true if now too small, so should be untreeified
           */
          final boolean removeTreeNode(TreeNode<K,V> p) {
              TreeNode<K,V> next = (TreeNode<K,V>)p.next;
              TreeNode<K,V> pred = p.prev;  // unlink traversal pointers
              TreeNode<K,V> r, rl;
              if (pred == null)
                  first = next;
              else
                  pred.next = next;
              if (next != null)
                  next.prev = pred;
              if (first == null) {
                  root = null;
                  return true;
              }
              if ((r = root) == null || r.right == null || // too small
                  (rl = r.left) == null || rl.left == null)
                  return true;
              lockRoot();
              try {
                  TreeNode<K,V> replacement;
                  TreeNode<K,V> pl = p.left;
                  TreeNode<K,V> pr = p.right;
                  if (pl != null && pr != null) {
                      TreeNode<K,V> s = pr, sl;
                      while ((sl = s.left) != null) // find successor
                          s = sl;
                      boolean c = s.red; s.red = p.red; p.red = c; // swap colors
                      TreeNode<K,V> sr = s.right;
                      TreeNode<K,V> pp = p.parent;
                      if (s == pr) { // p was s's direct parent
                          p.parent = s;
                          s.right = p;
                      }
                      else {
                          TreeNode<K,V> sp = s.parent;
                          if ((p.parent = sp) != null) {
                              if (s == sp.left)
                                  sp.left = p;
                              else
                                  sp.right = p;
                          }
                          if ((s.right = pr) != null)
                              pr.parent = s;
                      }
                      p.left = null;
                      if ((p.right = sr) != null)
                          sr.parent = p;
                      if ((s.left = pl) != null)
                          pl.parent = s;
                      if ((s.parent = pp) == null)
                          r = s;
                      else if (p == pp.left)
                          pp.left = s;
                      else
                          pp.right = s;
                      if (sr != null)
                          replacement = sr;
                      else
                          replacement = p;
                  }
                  else if (pl != null)
                      replacement = pl;
                  else if (pr != null)
                      replacement = pr;
                  else
                      replacement = p;
                  if (replacement != p) {
                      TreeNode<K,V> pp = replacement.parent = p.parent;
                      if (pp == null)
                          r = replacement;
                      else if (p == pp.left)
                          pp.left = replacement;
                      else
                          pp.right = replacement;
                      p.left = p.right = p.parent = null;
                  }
  
                  root = (p.red) ? r : balanceDeletion(r, replacement);
  
                  if (p == replacement) {  // detach pointers
                      TreeNode<K,V> pp;
                      if ((pp = p.parent) != null) {
                          if (p == pp.left)
                              pp.left = null;
                          else if (p == pp.right)
                              pp.right = null;
                          p.parent = null;
                      }
                  }
              } finally {
                  unlockRoot();
              }
              assert checkInvariants(root);
              return false;
          }
  
          /* ------------------------------------------------------------ */
          // Red-black tree methods, all adapted from CLR
  
          static <K,V> TreeNode<K,V> rotateLeft(TreeNode<K,V> root,
                                                TreeNode<K,V> p) {
              TreeNode<K,V> r, pp, rl;
              if (p != null && (r = p.right) != null) {
                  if ((rl = p.right = r.left) != null)
                      rl.parent = p;
                  if ((pp = r.parent = p.parent) == null)
                      (root = r).red = false;
                  else if (pp.left == p)
                      pp.left = r;
                  else
                      pp.right = r;
                  r.left = p;
                  p.parent = r;
              }
              return root;
          }
  
          static <K,V> TreeNode<K,V> rotateRight(TreeNode<K,V> root,
                                                 TreeNode<K,V> p) {
              TreeNode<K,V> l, pp, lr;
              if (p != null && (l = p.left) != null) {
                  if ((lr = p.left = l.right) != null)
                      lr.parent = p;
                  if ((pp = l.parent = p.parent) == null)
                      (root = l).red = false;
                  else if (pp.right == p)
                      pp.right = l;
                  else
                      pp.left = l;
                  l.right = p;
                  p.parent = l;
              }
              return root;
          }
  
          static <K,V> TreeNode<K,V> balanceInsertion(TreeNode<K,V> root,
                                                      TreeNode<K,V> x) {
              x.red = true;
              for (TreeNode<K,V> xp, xpp, xppl, xppr;;) {
                  if ((xp = x.parent) == null) {
                      x.red = false;
                      return x;
                  }
                  else if (!xp.red || (xpp = xp.parent) == null)
                      return root;
                  if (xp == (xppl = xpp.left)) {
                      if ((xppr = xpp.right) != null && xppr.red) {
                          xppr.red = false;
                          xp.red = false;
                          xpp.red = true;
                          x = xpp;
                      }
                      else {
                          if (x == xp.right) {
                              root = rotateLeft(root, x = xp);
                              xpp = (xp = x.parent) == null ? null : xp.parent;
                          }
                          if (xp != null) {
                              xp.red = false;
                              if (xpp != null) {
                                  xpp.red = true;
                                  root = rotateRight(root, xpp);
                              }
                          }
                      }
                  }
                  else {
                      if (xppl != null && xppl.red) {
                          xppl.red = false;
                          xp.red = false;
                          xpp.red = true;
                          x = xpp;
                      }
                      else {
                          if (x == xp.left) {
                              root = rotateRight(root, x = xp);
                              xpp = (xp = x.parent) == null ? null : xp.parent;
                          }
                          if (xp != null) {
                              xp.red = false;
                              if (xpp != null) {
                                  xpp.red = true;
                                  root = rotateLeft(root, xpp);
                              }
                          }
                      }
                  }
              }
          }
  
          static <K,V> TreeNode<K,V> balanceDeletion(TreeNode<K,V> root,
                                                     TreeNode<K,V> x) {
              for (TreeNode<K,V> xp, xpl, xpr;;) {
                  if (x == null || x == root)
                      return root;
                  else if ((xp = x.parent) == null) {
                      x.red = false;
                      return x;
                  }
                  else if (x.red) {
                      x.red = false;
                      return root;
                  }
                  else if ((xpl = xp.left) == x) {
                      if ((xpr = xp.right) != null && xpr.red) {
                          xpr.red = false;
                          xp.red = true;
                          root = rotateLeft(root, xp);
                          xpr = (xp = x.parent) == null ? null : xp.right;
                      }
                      if (xpr == null)
                          x = xp;
                      else {
                          TreeNode<K,V> sl = xpr.left, sr = xpr.right;
                          if ((sr == null || !sr.red) &&
                              (sl == null || !sl.red)) {
                              xpr.red = true;
                              x = xp;
                          }
                          else {
                              if (sr == null || !sr.red) {
                                  if (sl != null)
                                      sl.red = false;
                                  xpr.red = true;
                                  root = rotateRight(root, xpr);
                                  xpr = (xp = x.parent) == null ?
                                      null : xp.right;
                              }
                              if (xpr != null) {
                                  xpr.red = (xp == null) ? false : xp.red;
                                  if ((sr = xpr.right) != null)
                                      sr.red = false;
                              }
                              if (xp != null) {
                                  xp.red = false;
                                  root = rotateLeft(root, xp);
                              }
                              x = root;
                          }
                      }
                  }
                  else { // symmetric
                      if (xpl != null && xpl.red) {
                          xpl.red = false;
                          xp.red = true;
                          root = rotateRight(root, xp);
                          xpl = (xp = x.parent) == null ? null : xp.left;
                      }
                      if (xpl == null)
                          x = xp;
                      else {
                          TreeNode<K,V> sl = xpl.left, sr = xpl.right;
                          if ((sl == null || !sl.red) &&
                              (sr == null || !sr.red)) {
                              xpl.red = true;
                              x = xp;
                          }
                          else {
                              if (sl == null || !sl.red) {
                                  if (sr != null)
                                      sr.red = false;
                                  xpl.red = true;
                                  root = rotateLeft(root, xpl);
                                  xpl = (xp = x.parent) == null ?
                                      null : xp.left;
                              }
                              if (xpl != null) {
                                  xpl.red = (xp == null) ? false : xp.red;
                                  if ((sl = xpl.left) != null)
                                      sl.red = false;
                              }
                              if (xp != null) {
                                  xp.red = false;
                                  root = rotateRight(root, xp);
                              }
                              x = root;
                          }
                      }
                  }
              }
          }
  
          /**
           * Checks invariants recursively for the tree of Nodes rooted at t.
           */
          static <K,V> boolean checkInvariants(TreeNode<K,V> t) {
              TreeNode<K,V> tp = t.parent, tl = t.left, tr = t.right,
                  tb = t.prev, tn = (TreeNode<K,V>)t.next;
              if (tb != null && tb.next != t)
                  return false;
              if (tn != null && tn.prev != t)
                  return false;
              if (tp != null && t != tp.left && t != tp.right)
                  return false;
              if (tl != null && (tl.parent != t || tl.hash > t.hash))
                  return false;
              if (tr != null && (tr.parent != t || tr.hash < t.hash))
                  return false;
              if (t.red && tl != null && tl.red && tr != null && tr.red)
                  return false;
              if (tl != null && !checkInvariants(tl))
                  return false;
              if (tr != null && !checkInvariants(tr))
                  return false;
              return true;
          }
  
          private static final sun.misc.Unsafe U = sun.misc.Unsafe.getUnsafe();
          private static final long LOCKSTATE;
          static {
              try {
                  LOCKSTATE = U.objectFieldOffset
                      (TreeBin.class.getDeclaredField("lockState"));
              } catch (ReflectiveOperationException e) {
                  throw new Error(e);
              }
          }
      }
  
      /* ----------------Table Traversal -------------- */
  
      /**
       * Records the table, its length, and current traversal index for a
       * traverser that must process a region of a forwarded table before
       * proceeding with current table.
       */
      static final class TableStack<K,V> {
          int length;
          int index;
          Node<K,V>[] tab;
          TableStack<K,V> next;
      }
  
      /**
       * Encapsulates traversal for methods such as containsValue; also
       * serves as a base class for other iterators and spliterators.
       *
       * Method advance visits once each still-valid node that was
       * reachable upon iterator construction. It might miss some that
       * were added to a bin after the bin was visited, which is OK wrt
       * consistency guarantees. Maintaining this property in the face
       * of possible ongoing resizes requires a fair amount of
       * bookkeeping state that is difficult to optimize away amidst
       * volatile accesses.  Even so, traversal maintains reasonable
       * throughput.
       *
       * Normally, iteration proceeds bin-by-bin traversing lists.
       * However, if the table has been resized, then all future steps
       * must traverse both the bin at the current index as well as at
       * (index + baseSize); and so on for further resizings. To
       * paranoically cope with potential sharing by users of iterators
       * across threads, iteration terminates if a bounds checks fails
       * for a table read.
       */
      static class Traverser<K,V> {
          Node<K,V>[] tab;        // current table; updated if resized
          Node<K,V> next;         // the next entry to use
          TableStack<K,V> stack, spare; // to save/restore on ForwardingNodes
          int index;              // index of bin to use next
          int baseIndex;          // current index of initial table
          int baseLimit;          // index bound for initial table
          final int baseSize;     // initial table size
  
          Traverser(Node<K,V>[] tab, int size, int index, int limit) {
              this.tab = tab;
              this.baseSize = size;
              this.baseIndex = this.index = index;
              this.baseLimit = limit;
              this.next = null;
          }
  
          /**
           * Advances if possible, returning next valid node, or null if none.
           */
          final Node<K,V> advance() {
              Node<K,V> e;
              if ((e = next) != null)
                  e = e.next;
              for (;;) {
                  Node<K,V>[] t; int i, n;  // must use locals in checks
                  if (e != null)
                      return next = e;
                  if (baseIndex >= baseLimit || (t = tab) == null ||
                      (n = t.length) <= (i = index) || i < 0)
                      return next = null;
                  if ((e = tabAt(t, i)) != null && e.hash < 0) {
                      if (e instanceof ForwardingNode) {
                          tab = ((ForwardingNode<K,V>)e).nextTable;
                          e = null;
                          pushState(t, i, n);
                          continue;
                      }
                      else if (e instanceof TreeBin)
                          e = ((TreeBin<K,V>)e).first;
                      else
                          e = null;
                  }
                  if (stack != null)
                      recoverState(n);
                  else if ((index = i + baseSize) >= n)
                      index = ++baseIndex; // visit upper slots if present
              }
          }
  
          /**
           * Saves traversal state upon encountering a forwarding node.
           */
          private void pushState(Node<K,V>[] t, int i, int n) {
              TableStack<K,V> s = spare;  // reuse if possible
              if (s != null)
                  spare = s.next;
              else
                  s = new TableStack<K,V>();
              s.tab = t;
              s.length = n;
              s.index = i;
              s.next = stack;
              stack = s;
          }
  
          /**
           * Possibly pops traversal state.
           *
           * @param n length of current table
           */
          private void recoverState(int n) {
              TableStack<K,V> s; int len;
              while ((s = stack) != null && (index += (len = s.length)) >= n) {
                  n = len;
                  index = s.index;
                  tab = s.tab;
                  s.tab = null;
                  TableStack<K,V> next = s.next;
                  s.next = spare; // save for reuse
                  stack = next;
                  spare = s;
              }
              if (s == null && (index += baseSize) >= n)
                  index = ++baseIndex;
          }
      }
  
      /**
       * Base of key, value, and entry Iterators. Adds fields to
       * Traverser to support iterator.remove.
       */
      static class BaseIterator<K,V> extends Traverser<K,V> {
          final ConcurrentHashMap<K,V> map;
          Node<K,V> lastReturned;
          BaseIterator(Node<K,V>[] tab, int size, int index, int limit,
                      ConcurrentHashMap<K,V> map) {
              super(tab, size, index, limit);
              this.map = map;
              advance();
          }
  
          public final boolean hasNext() { return next != null; }
          public final boolean hasMoreElements() { return next != null; }
  
          public final void remove() {
              Node<K,V> p;
              if ((p = lastReturned) == null)
                  throw new IllegalStateException();
              lastReturned = null;
              map.replaceNode(p.key, null, null);
          }
      }
  
      static final class KeyIterator<K,V> extends BaseIterator<K,V>
          implements Iterator<K>, Enumeration<K> {
          KeyIterator(Node<K,V>[] tab, int index, int size, int limit,
                      ConcurrentHashMap<K,V> map) {
              super(tab, index, size, limit, map);
          }
  
          public final K next() {
              Node<K,V> p;
              if ((p = next) == null)
                  throw new NoSuchElementException();
              K k = p.key;
              lastReturned = p;
              advance();
              return k;
          }
  
          public final K nextElement() { return next(); }
      }
  
      static final class ValueIterator<K,V> extends BaseIterator<K,V>
          implements Iterator<V>, Enumeration<V> {
          ValueIterator(Node<K,V>[] tab, int index, int size, int limit,
                        ConcurrentHashMap<K,V> map) {
              super(tab, index, size, limit, map);
          }
  
          public final V next() {
              Node<K,V> p;
              if ((p = next) == null)
                  throw new NoSuchElementException();
              V v = p.val;
              lastReturned = p;
              advance();
              return v;
          }
  
          public final V nextElement() { return next(); }
      }
  
      static final class EntryIterator<K,V> extends BaseIterator<K,V>
          implements Iterator<Entry<K,V>> {
          EntryIterator(Node<K,V>[] tab, int index, int size, int limit,
                        ConcurrentHashMap<K,V> map) {
              super(tab, index, size, limit, map);
          }
  
          public final Entry<K,V> next() {
              Node<K,V> p;
              if ((p = next) == null)
                  throw new NoSuchElementException();
              K k = p.key;
              V v = p.val;
              lastReturned = p;
              advance();
              return new MapEntry<K,V>(k, v, map);
          }
      }
  
      /**
       * Exported Entry for EntryIterator.
       */
      static final class MapEntry<K,V> implements Entry<K,V> {
          final K key; // non-null
          V val;       // non-null
          final ConcurrentHashMap<K,V> map;
          MapEntry(K key, V val, ConcurrentHashMap<K,V> map) {
              this.key = key;
              this.val = val;
              this.map = map;
          }
          public K getKey()        { return key; }
          public V getValue()      { return val; }
          public int hashCode()    { return key.hashCode() ^ val.hashCode(); }
          public String toString() {
              return Helpers.mapEntryToString(key, val);
          }
  
          public boolean equals(Object o) {
              Object k, v; Entry<?,?> e;
              return ((o instanceof Map.Entry) &&
                      (k = (e = (Entry<?,?>)o).getKey()) != null &&
                      (v = e.getValue()) != null &&
                      (k == key || k.equals(key)) &&
                      (v == val || v.equals(val)));
          }
  
          /**
           * Sets our entry's value and writes through to the map. The
           * value to return is somewhat arbitrary here. Since we do not
           * necessarily track asynchronous changes, the most recent
           * "previous" value could be different from what we return (or
           * could even have been removed, in which case the put will
           * re-establish). We do not and cannot guarantee more.
           */
          public V setValue(V value) {
              if (value == null) throw new NullPointerException();
              V v = val;
              val = value;
              map.put(key, value);
              return v;
          }
      }
  
      static final class KeySpliterator<K,V> extends Traverser<K,V>
          implements Spliterator<K> {
          long est;               // size estimate
          KeySpliterator(Node<K,V>[] tab, int size, int index, int limit,
                         long est) {
              super(tab, size, index, limit);
              this.est = est;
          }
  
          public KeySpliterator<K,V> trySplit() {
              int i, f, h;
              return (h = ((i = baseIndex) + (f = baseLimit)) >>> 1) <= i ? null :
                  new KeySpliterator<K,V>(tab, baseSize, baseLimit = h,
                                          f, est >>>= 1);
          }
  
          public void forEachRemaining(Consumer<? super K> action) {
              if (action == null) throw new NullPointerException();
              for (Node<K,V> p; (p = advance()) != null;)
                  action.accept(p.key);
          }
  
          public boolean tryAdvance(Consumer<? super K> action) {
              if (action == null) throw new NullPointerException();
              Node<K,V> p;
              if ((p = advance()) == null)
                  return false;
              action.accept(p.key);
              return true;
          }
  
          public long estimateSize() { return est; }
  
          public int characteristics() {
              return Spliterator.DISTINCT | Spliterator.CONCURRENT |
                  Spliterator.NONNULL;
          }
      }
  
      static final class ValueSpliterator<K,V> extends Traverser<K,V>
          implements Spliterator<V> {
          long est;               // size estimate
          ValueSpliterator(Node<K,V>[] tab, int size, int index, int limit,
                           long est) {
              super(tab, size, index, limit);
              this.est = est;
          }
  
          public ValueSpliterator<K,V> trySplit() {
              int i, f, h;
              return (h = ((i = baseIndex) + (f = baseLimit)) >>> 1) <= i ? null :
                  new ValueSpliterator<K,V>(tab, baseSize, baseLimit = h,
                                            f, est >>>= 1);
          }
  
          public void forEachRemaining(Consumer<? super V> action) {
              if (action == null) throw new NullPointerException();
              for (Node<K,V> p; (p = advance()) != null;)
                  action.accept(p.val);
          }
  
          public boolean tryAdvance(Consumer<? super V> action) {
              if (action == null) throw new NullPointerException();
              Node<K,V> p;
              if ((p = advance()) == null)
                  return false;
              action.accept(p.val);
              return true;
          }
  
          public long estimateSize() { return est; }
  
          public int characteristics() {
              return Spliterator.CONCURRENT | Spliterator.NONNULL;
          }
      }
  
      static final class EntrySpliterator<K,V> extends Traverser<K,V>
          implements Spliterator<Entry<K,V>> {
          final ConcurrentHashMap<K,V> map; // To export MapEntry
          long est;               // size estimate
          EntrySpliterator(Node<K,V>[] tab, int size, int index, int limit,
                           long est, ConcurrentHashMap<K,V> map) {
              super(tab, size, index, limit);
              this.map = map;
              this.est = est;
          }
  
          public EntrySpliterator<K,V> trySplit() {
              int i, f, h;
              return (h = ((i = baseIndex) + (f = baseLimit)) >>> 1) <= i ? null :
                  new EntrySpliterator<K,V>(tab, baseSize, baseLimit = h,
                                            f, est >>>= 1, map);
          }
  
          public void forEachRemaining(Consumer<? super Entry<K,V>> action) {
              if (action == null) throw new NullPointerException();
              for (Node<K,V> p; (p = advance()) != null; )
                  action.accept(new MapEntry<K,V>(p.key, p.val, map));
          }
  
          public boolean tryAdvance(Consumer<? super Entry<K,V>> action) {
              if (action == null) throw new NullPointerException();
              Node<K,V> p;
              if ((p = advance()) == null)
                  return false;
              action.accept(new MapEntry<K,V>(p.key, p.val, map));
              return true;
          }
  
          public long estimateSize() { return est; }
  
          public int characteristics() {
              return Spliterator.DISTINCT | Spliterator.CONCURRENT |
                  Spliterator.NONNULL;
          }
      }
  
      // Parallel bulk operations
  
      /**
       * Computes initial batch value for bulk tasks. The returned value
       * is approximately exp2 of the number of times (minus one) to
       * split task by two before executing leaf action. This value is
       * faster to compute and more convenient to use as a guide to
       * splitting than is the depth, since it is used while dividing by
       * two anyway.
       */
      final int batchFor(long b) {
          long n;
          if (b == Long.MAX_VALUE || (n = sumCount()) <= 1L || n < b)
              return 0;
          int sp = ForkJoinPool.getCommonPoolParallelism() << 2; // slack of 4
          return (b <= 0L || (n /= b) >= sp) ? sp : (int)n;
      }
  
      /**
       * Performs the given action for each (key, value).
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param action the action
       * @since 1.8
       */
      public void forEach(long parallelismThreshold,
                          BiConsumer<? super K,? super V> action) {
          if (action == null) throw new NullPointerException();
          new ForEachMappingTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               action).invoke();
      }
  
      /**
       * Performs the given action for each non-null transformation
       * of each (key, value).
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element, or null if there is no transformation (in
       * which case the action is not applied)
       * @param action the action
       * @param <U> the return type of the transformer
       * @since 1.8
       */
      public <U> void forEach(long parallelismThreshold,
                              BiFunction<? super K, ? super V, ? extends U> transformer,
                              Consumer<? super U> action) {
          if (transformer == null || action == null)
              throw new NullPointerException();
          new ForEachTransformedMappingTask<K,V,U>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               transformer, action).invoke();
      }
  
      /**
       * Returns a non-null result from applying the given search
       * function on each (key, value), or null if none.  Upon
       * success, further element processing is suppressed and the
       * results of any other parallel invocations of the search
       * function are ignored.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param searchFunction a function returning a non-null
       * result on success, else null
       * @param <U> the return type of the search function
       * @return a non-null result from applying the given search
       * function on each (key, value), or null if none
       * @since 1.8
       */
      public <U> U search(long parallelismThreshold,
                          BiFunction<? super K, ? super V, ? extends U> searchFunction) {
          if (searchFunction == null) throw new NullPointerException();
          return new SearchMappingsTask<K,V,U>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               searchFunction, new AtomicReference<U>()).invoke();
      }
  
      /**
       * Returns the result of accumulating the given transformation
       * of all (key, value) pairs using the given reducer to
       * combine values, or null if none.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element, or null if there is no transformation (in
       * which case it is not combined)
       * @param reducer a commutative associative combining function
       * @param <U> the return type of the transformer
       * @return the result of accumulating the given transformation
       * of all (key, value) pairs
       * @since 1.8
       */
      public <U> U reduce(long parallelismThreshold,
                          BiFunction<? super K, ? super V, ? extends U> transformer,
                          BiFunction<? super U, ? super U, ? extends U> reducer) {
          if (transformer == null || reducer == null)
              throw new NullPointerException();
          return new MapReduceMappingsTask<K,V,U>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, transformer, reducer).invoke();
      }
  
      /**
       * Returns the result of accumulating the given transformation
       * of all (key, value) pairs using the given reducer to
       * combine values, and the given basis as an identity value.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element
       * @param basis the identity (initial default value) for the reduction
       * @param reducer a commutative associative combining function
       * @return the result of accumulating the given transformation
       * of all (key, value) pairs
       * @since 1.8
       */
      public double reduceToDouble(long parallelismThreshold,
                                   ToDoubleBiFunction<? super K, ? super V> transformer,
                                   double basis,
                                   DoubleBinaryOperator reducer) {
          if (transformer == null || reducer == null)
              throw new NullPointerException();
          return new MapReduceMappingsToDoubleTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, transformer, basis, reducer).invoke();
      }
  
      /**
       * Returns the result of accumulating the given transformation
       * of all (key, value) pairs using the given reducer to
       * combine values, and the given basis as an identity value.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element
       * @param basis the identity (initial default value) for the reduction
       * @param reducer a commutative associative combining function
       * @return the result of accumulating the given transformation
       * of all (key, value) pairs
       * @since 1.8
       */
      public long reduceToLong(long parallelismThreshold,
                               ToLongBiFunction<? super K, ? super V> transformer,
                               long basis,
                               LongBinaryOperator reducer) {
          if (transformer == null || reducer == null)
              throw new NullPointerException();
          return new MapReduceMappingsToLongTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, transformer, basis, reducer).invoke();
      }
  
      /**
       * Returns the result of accumulating the given transformation
       * of all (key, value) pairs using the given reducer to
       * combine values, and the given basis as an identity value.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element
       * @param basis the identity (initial default value) for the reduction
       * @param reducer a commutative associative combining function
       * @return the result of accumulating the given transformation
       * of all (key, value) pairs
       * @since 1.8
       */
      public int reduceToInt(long parallelismThreshold,
                             ToIntBiFunction<? super K, ? super V> transformer,
                             int basis,
                             IntBinaryOperator reducer) {
          if (transformer == null || reducer == null)
              throw new NullPointerException();
          return new MapReduceMappingsToIntTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, transformer, basis, reducer).invoke();
      }
  
      /**
       * Performs the given action for each key.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param action the action
       * @since 1.8
       */
      public void forEachKey(long parallelismThreshold,
                             Consumer<? super K> action) {
          if (action == null) throw new NullPointerException();
          new ForEachKeyTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               action).invoke();
      }
  
      /**
       * Performs the given action for each non-null transformation
       * of each key.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element, or null if there is no transformation (in
       * which case the action is not applied)
       * @param action the action
       * @param <U> the return type of the transformer
       * @since 1.8
       */
      public <U> void forEachKey(long parallelismThreshold,
                                 Function<? super K, ? extends U> transformer,
                                 Consumer<? super U> action) {
          if (transformer == null || action == null)
              throw new NullPointerException();
          new ForEachTransformedKeyTask<K,V,U>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               transformer, action).invoke();
      }
  
      /**
       * Returns a non-null result from applying the given search
       * function on each key, or null if none. Upon success,
       * further element processing is suppressed and the results of
       * any other parallel invocations of the search function are
       * ignored.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param searchFunction a function returning a non-null
       * result on success, else null
       * @param <U> the return type of the search function
       * @return a non-null result from applying the given search
       * function on each key, or null if none
       * @since 1.8
       */
      public <U> U searchKeys(long parallelismThreshold,
                              Function<? super K, ? extends U> searchFunction) {
          if (searchFunction == null) throw new NullPointerException();
          return new SearchKeysTask<K,V,U>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               searchFunction, new AtomicReference<U>()).invoke();
      }
  
      /**
       * Returns the result of accumulating all keys using the given
       * reducer to combine values, or null if none.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param reducer a commutative associative combining function
       * @return the result of accumulating all keys using the given
       * reducer to combine values, or null if none
       * @since 1.8
       */
      public K reduceKeys(long parallelismThreshold,
                          BiFunction<? super K, ? super K, ? extends K> reducer) {
          if (reducer == null) throw new NullPointerException();
          return new ReduceKeysTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, reducer).invoke();
      }
  
      /**
       * Returns the result of accumulating the given transformation
       * of all keys using the given reducer to combine values, or
       * null if none.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element, or null if there is no transformation (in
       * which case it is not combined)
       * @param reducer a commutative associative combining function
       * @param <U> the return type of the transformer
       * @return the result of accumulating the given transformation
       * of all keys
       * @since 1.8
       */
      public <U> U reduceKeys(long parallelismThreshold,
                              Function<? super K, ? extends U> transformer,
           BiFunction<? super U, ? super U, ? extends U> reducer) {
          if (transformer == null || reducer == null)
              throw new NullPointerException();
          return new MapReduceKeysTask<K,V,U>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, transformer, reducer).invoke();
      }
  
      /**
       * Returns the result of accumulating the given transformation
       * of all keys using the given reducer to combine values, and
       * the given basis as an identity value.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element
       * @param basis the identity (initial default value) for the reduction
       * @param reducer a commutative associative combining function
       * @return the result of accumulating the given transformation
       * of all keys
       * @since 1.8
       */
      public double reduceKeysToDouble(long parallelismThreshold,
                                       ToDoubleFunction<? super K> transformer,
                                       double basis,
                                       DoubleBinaryOperator reducer) {
          if (transformer == null || reducer == null)
              throw new NullPointerException();
          return new MapReduceKeysToDoubleTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, transformer, basis, reducer).invoke();
      }
  
      /**
       * Returns the result of accumulating the given transformation
       * of all keys using the given reducer to combine values, and
       * the given basis as an identity value.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element
       * @param basis the identity (initial default value) for the reduction
       * @param reducer a commutative associative combining function
       * @return the result of accumulating the given transformation
       * of all keys
       * @since 1.8
       */
      public long reduceKeysToLong(long parallelismThreshold,
                                   ToLongFunction<? super K> transformer,
                                   long basis,
                                   LongBinaryOperator reducer) {
          if (transformer == null || reducer == null)
              throw new NullPointerException();
          return new MapReduceKeysToLongTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, transformer, basis, reducer).invoke();
      }
  
      /**
       * Returns the result of accumulating the given transformation
       * of all keys using the given reducer to combine values, and
       * the given basis as an identity value.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element
       * @param basis the identity (initial default value) for the reduction
       * @param reducer a commutative associative combining function
       * @return the result of accumulating the given transformation
       * of all keys
       * @since 1.8
       */
      public int reduceKeysToInt(long parallelismThreshold,
                                 ToIntFunction<? super K> transformer,
                                 int basis,
                                 IntBinaryOperator reducer) {
          if (transformer == null || reducer == null)
              throw new NullPointerException();
          return new MapReduceKeysToIntTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, transformer, basis, reducer).invoke();
      }
  
      /**
       * Performs the given action for each value.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param action the action
       * @since 1.8
       */
      public void forEachValue(long parallelismThreshold,
                               Consumer<? super V> action) {
          if (action == null)
              throw new NullPointerException();
          new ForEachValueTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               action).invoke();
      }
  
      /**
       * Performs the given action for each non-null transformation
       * of each value.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element, or null if there is no transformation (in
       * which case the action is not applied)
       * @param action the action
       * @param <U> the return type of the transformer
       * @since 1.8
       */
      public <U> void forEachValue(long parallelismThreshold,
                                   Function<? super V, ? extends U> transformer,
                                   Consumer<? super U> action) {
          if (transformer == null || action == null)
              throw new NullPointerException();
          new ForEachTransformedValueTask<K,V,U>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               transformer, action).invoke();
      }
  
      /**
       * Returns a non-null result from applying the given search
       * function on each value, or null if none.  Upon success,
       * further element processing is suppressed and the results of
       * any other parallel invocations of the search function are
       * ignored.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param searchFunction a function returning a non-null
       * result on success, else null
       * @param <U> the return type of the search function
       * @return a non-null result from applying the given search
       * function on each value, or null if none
       * @since 1.8
       */
      public <U> U searchValues(long parallelismThreshold,
                                Function<? super V, ? extends U> searchFunction) {
          if (searchFunction == null) throw new NullPointerException();
          return new SearchValuesTask<K,V,U>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               searchFunction, new AtomicReference<U>()).invoke();
      }
  
      /**
       * Returns the result of accumulating all values using the
       * given reducer to combine values, or null if none.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param reducer a commutative associative combining function
       * @return the result of accumulating all values
       * @since 1.8
       */
      public V reduceValues(long parallelismThreshold,
                            BiFunction<? super V, ? super V, ? extends V> reducer) {
          if (reducer == null) throw new NullPointerException();
          return new ReduceValuesTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, reducer).invoke();
      }
  
      /**
       * Returns the result of accumulating the given transformation
       * of all values using the given reducer to combine values, or
       * null if none.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element, or null if there is no transformation (in
       * which case it is not combined)
       * @param reducer a commutative associative combining function
       * @param <U> the return type of the transformer
       * @return the result of accumulating the given transformation
       * of all values
       * @since 1.8
       */
      public <U> U reduceValues(long parallelismThreshold,
                                Function<? super V, ? extends U> transformer,
                                BiFunction<? super U, ? super U, ? extends U> reducer) {
          if (transformer == null || reducer == null)
              throw new NullPointerException();
          return new MapReduceValuesTask<K,V,U>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, transformer, reducer).invoke();
      }
  
      /**
       * Returns the result of accumulating the given transformation
       * of all values using the given reducer to combine values,
       * and the given basis as an identity value.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element
       * @param basis the identity (initial default value) for the reduction
       * @param reducer a commutative associative combining function
       * @return the result of accumulating the given transformation
       * of all values
       * @since 1.8
       */
      public double reduceValuesToDouble(long parallelismThreshold,
                                         ToDoubleFunction<? super V> transformer,
                                         double basis,
                                         DoubleBinaryOperator reducer) {
          if (transformer == null || reducer == null)
              throw new NullPointerException();
          return new MapReduceValuesToDoubleTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, transformer, basis, reducer).invoke();
      }
  
      /**
       * Returns the result of accumulating the given transformation
       * of all values using the given reducer to combine values,
       * and the given basis as an identity value.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element
       * @param basis the identity (initial default value) for the reduction
       * @param reducer a commutative associative combining function
       * @return the result of accumulating the given transformation
       * of all values
       * @since 1.8
       */
      public long reduceValuesToLong(long parallelismThreshold,
                                     ToLongFunction<? super V> transformer,
                                     long basis,
                                     LongBinaryOperator reducer) {
          if (transformer == null || reducer == null)
              throw new NullPointerException();
          return new MapReduceValuesToLongTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, transformer, basis, reducer).invoke();
      }
  
      /**
       * Returns the result of accumulating the given transformation
       * of all values using the given reducer to combine values,
       * and the given basis as an identity value.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element
       * @param basis the identity (initial default value) for the reduction
       * @param reducer a commutative associative combining function
       * @return the result of accumulating the given transformation
       * of all values
       * @since 1.8
       */
      public int reduceValuesToInt(long parallelismThreshold,
                                   ToIntFunction<? super V> transformer,
                                   int basis,
                                   IntBinaryOperator reducer) {
          if (transformer == null || reducer == null)
              throw new NullPointerException();
          return new MapReduceValuesToIntTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, transformer, basis, reducer).invoke();
      }
  
      /**
       * Performs the given action for each entry.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param action the action
       * @since 1.8
       */
      public void forEachEntry(long parallelismThreshold,
                               Consumer<? super Entry<K,V>> action) {
          if (action == null) throw new NullPointerException();
          new ForEachEntryTask<K,V>(null, batchFor(parallelismThreshold), 0, 0, table,
                                    action).invoke();
      }
  
      /**
       * Performs the given action for each non-null transformation
       * of each entry.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element, or null if there is no transformation (in
       * which case the action is not applied)
       * @param action the action
       * @param <U> the return type of the transformer
       * @since 1.8
       */
      public <U> void forEachEntry(long parallelismThreshold,
                                   Function<Entry<K,V>, ? extends U> transformer,
                                   Consumer<? super U> action) {
          if (transformer == null || action == null)
              throw new NullPointerException();
          new ForEachTransformedEntryTask<K,V,U>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               transformer, action).invoke();
      }
  
      /**
       * Returns a non-null result from applying the given search
       * function on each entry, or null if none.  Upon success,
       * further element processing is suppressed and the results of
       * any other parallel invocations of the search function are
       * ignored.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param searchFunction a function returning a non-null
       * result on success, else null
       * @param <U> the return type of the search function
       * @return a non-null result from applying the given search
       * function on each entry, or null if none
       * @since 1.8
       */
      public <U> U searchEntries(long parallelismThreshold,
                                 Function<Entry<K,V>, ? extends U> searchFunction) {
          if (searchFunction == null) throw new NullPointerException();
          return new SearchEntriesTask<K,V,U>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               searchFunction, new AtomicReference<U>()).invoke();
      }
  
      /**
       * Returns the result of accumulating all entries using the
       * given reducer to combine values, or null if none.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param reducer a commutative associative combining function
       * @return the result of accumulating all entries
       * @since 1.8
       */
      public Entry<K,V> reduceEntries(long parallelismThreshold,
                                          BiFunction<Entry<K,V>, Entry<K,V>, ? extends Entry<K,V>> reducer) {
          if (reducer == null) throw new NullPointerException();
          return new ReduceEntriesTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, reducer).invoke();
      }
  
      /**
       * Returns the result of accumulating the given transformation
       * of all entries using the given reducer to combine values,
       * or null if none.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element, or null if there is no transformation (in
       * which case it is not combined)
       * @param reducer a commutative associative combining function
       * @param <U> the return type of the transformer
       * @return the result of accumulating the given transformation
       * of all entries
       * @since 1.8
       */
      public <U> U reduceEntries(long parallelismThreshold,
                                 Function<Entry<K,V>, ? extends U> transformer,
                                 BiFunction<? super U, ? super U, ? extends U> reducer) {
          if (transformer == null || reducer == null)
              throw new NullPointerException();
          return new MapReduceEntriesTask<K,V,U>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, transformer, reducer).invoke();
      }
  
      /**
       * Returns the result of accumulating the given transformation
       * of all entries using the given reducer to combine values,
       * and the given basis as an identity value.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element
       * @param basis the identity (initial default value) for the reduction
       * @param reducer a commutative associative combining function
       * @return the result of accumulating the given transformation
       * of all entries
       * @since 1.8
       */
      public double reduceEntriesToDouble(long parallelismThreshold,
                                          ToDoubleFunction<Entry<K,V>> transformer,
                                          double basis,
                                          DoubleBinaryOperator reducer) {
          if (transformer == null || reducer == null)
              throw new NullPointerException();
          return new MapReduceEntriesToDoubleTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, transformer, basis, reducer).invoke();
      }
  
      /**
       * Returns the result of accumulating the given transformation
       * of all entries using the given reducer to combine values,
       * and the given basis as an identity value.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element
       * @param basis the identity (initial default value) for the reduction
       * @param reducer a commutative associative combining function
       * @return the result of accumulating the given transformation
       * of all entries
       * @since 1.8
       */
      public long reduceEntriesToLong(long parallelismThreshold,
                                      ToLongFunction<Entry<K,V>> transformer,
                                      long basis,
                                      LongBinaryOperator reducer) {
          if (transformer == null || reducer == null)
              throw new NullPointerException();
          return new MapReduceEntriesToLongTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, transformer, basis, reducer).invoke();
      }
  
      /**
       * Returns the result of accumulating the given transformation
       * of all entries using the given reducer to combine values,
       * and the given basis as an identity value.
       *
       * @param parallelismThreshold the (estimated) number of elements
       * needed for this operation to be executed in parallel
       * @param transformer a function returning the transformation
       * for an element
       * @param basis the identity (initial default value) for the reduction
       * @param reducer a commutative associative combining function
       * @return the result of accumulating the given transformation
       * of all entries
       * @since 1.8
       */
      public int reduceEntriesToInt(long parallelismThreshold,
                                    ToIntFunction<Entry<K,V>> transformer,
                                    int basis,
                                    IntBinaryOperator reducer) {
          if (transformer == null || reducer == null)
              throw new NullPointerException();
          return new MapReduceEntriesToIntTask<K,V>
              (null, batchFor(parallelismThreshold), 0, 0, table,
               null, transformer, basis, reducer).invoke();
      }
  
  
      /* ----------------Views -------------- */
  
      /**
       * Base class for views.
       */
      abstract static class CollectionView<K,V,E>
          implements Collection<E>, Serializable {
          private static final long serialVersionUID = 7249069246763182397L;
          final ConcurrentHashMap<K,V> map;
          CollectionView(ConcurrentHashMap<K,V> map)  { this.map = map; }
  
          /**
           * Returns the map backing this view.
           *
           * @return the map backing this view
           */
          public ConcurrentHashMap<K,V> getMap() { return map; }
  
          /**
           * Removes all of the elements from this view, by removing all
           * the mappings from the map backing this view.
           */
          public final void clear()      { map.clear(); }
          public final int size()        { return map.size(); }
          public final boolean isEmpty() { return map.isEmpty(); }
  
          // implementations below rely on concrete classes supplying these
          // abstract methods
          /**
           * Returns an iterator over the elements in this collection.
           *
           * <p>The returned iterator is
           * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
           *
           * @return an iterator over the elements in this collection
           */
          public abstract Iterator<E> iterator();
          public abstract boolean contains(Object o);
          public abstract boolean remove(Object o);
  
          private static final String OOME_MSG = "Required array size too large";
  
          public final Object[] toArray() {
              long sz = map.mappingCount();
              if (sz > MAX_ARRAY_SIZE)
                  throw new OutOfMemoryError(OOME_MSG);
              int n = (int)sz;
              Object[] r = new Object[n];
              int i = 0;
              for (E e : this) {
                  if (i == n) {
                      if (n >= MAX_ARRAY_SIZE)
                          throw new OutOfMemoryError(OOME_MSG);
                      if (n >= MAX_ARRAY_SIZE - (MAX_ARRAY_SIZE >>> 1) - 1)
                          n = MAX_ARRAY_SIZE;
                      else
                          n += (n >>> 1) + 1;
                      r = Arrays.copyOf(r, n);
                  }
                  r[i++] = e;
              }
              return (i == n) ? r : Arrays.copyOf(r, i);
          }
  
          @SuppressWarnings("unchecked")
          public final <T> T[] toArray(T[] a) {
              long sz = map.mappingCount();
              if (sz > MAX_ARRAY_SIZE)
                  throw new OutOfMemoryError(OOME_MSG);
              int m = (int)sz;
              T[] r = (a.length >= m) ? a :
                  (T[])java.lang.reflect.Array
                  .newInstance(a.getClass().getComponentType(), m);
              int n = r.length;
              int i = 0;
              for (E e : this) {
                  if (i == n) {
                      if (n >= MAX_ARRAY_SIZE)
                          throw new OutOfMemoryError(OOME_MSG);
                      if (n >= MAX_ARRAY_SIZE - (MAX_ARRAY_SIZE >>> 1) - 1)
                          n = MAX_ARRAY_SIZE;
                      else
                          n += (n >>> 1) + 1;
                      r = Arrays.copyOf(r, n);
                  }
                  r[i++] = (T)e;
              }
              if (a == r && i < n) {
                  r[i] = null; // null-terminate
                  return r;
              }
              return (i == n) ? r : Arrays.copyOf(r, i);
          }
  
          /**
           * Returns a string representation of this collection.
           * The string representation consists of the string representations
           * of the collection's elements in the order they are returned by
           * its iterator, enclosed in square brackets ({@code "[]"}).
           * Adjacent elements are separated by the characters {@code ", "}
           * (comma and space).  Elements are converted to strings as by
           * {@link String#valueOf(Object)}.
           *
           * @return a string representation of this collection
           */
          public final String toString() {
              StringBuilder sb = new StringBuilder();
              sb.append('[');
              Iterator<E> it = iterator();
              if (it.hasNext()) {
                  for (;;) {
                      Object e = it.next();
                      sb.append(e == this ? "(this Collection)" : e);
                      if (!it.hasNext())
                          break;
                      sb.append(',').append(' ');
                  }
              }
              return sb.append(']').toString();
          }
  
          public final boolean containsAll(Collection<?> c) {
              if (c != this) {
                  for (Object e : c) {
                      if (e == null || !contains(e))
                          return false;
                  }
              }
              return true;
          }
  
          public final boolean removeAll(Collection<?> c) {
              if (c == null) throw new NullPointerException();
              boolean modified = false;
              for (Iterator<E> it = iterator(); it.hasNext();) {
                  if (c.contains(it.next())) {
                      it.remove();
                      modified = true;
                  }
              }
              return modified;
          }
  
          public final boolean retainAll(Collection<?> c) {
              if (c == null) throw new NullPointerException();
              boolean modified = false;
              for (Iterator<E> it = iterator(); it.hasNext();) {
                  if (!c.contains(it.next())) {
                      it.remove();
                      modified = true;
                  }
              }
              return modified;
          }
  
      }
  
      /**
       * A view of a ConcurrentHashMap as a {@link Set} of keys, in
       * which additions may optionally be enabled by mapping to a
       * common value.  This class cannot be directly instantiated.
       * See {@link #keySet(Object) keySet(V)},
       * {@link #newKeySet() newKeySet()},
       * {@link #newKeySet(int) newKeySet(int)}.
       *
       * @since 1.8
       */
      public static class KeySetView<K,V> extends CollectionView<K,V,K>
          implements Set<K>, Serializable {
          private static final long serialVersionUID = 7249069246763182397L;
          private final V value;
          KeySetView(ConcurrentHashMap<K,V> map, V value) {  // non-public
              super(map);
              this.value = value;
          }
  
          /**
           * Returns the default mapped value for additions,
           * or {@code null} if additions are not supported.
           *
           * @return the default mapped value for additions, or {@code null}
           * if not supported
           */
          public V getMappedValue() { return value; }
  
          /**
           * {@inheritDoc}
           * @throws NullPointerException if the specified key is null
           */
          public boolean contains(Object o) { return map.containsKey(o); }
  
          /**
           * Removes the key from this map view, by removing the key (and its
           * corresponding value) from the backing map.  This method does
           * nothing if the key is not in the map.
           *
           * @param  o the key to be removed from the backing map
           * @return {@code true} if the backing map contained the specified key
           * @throws NullPointerException if the specified key is null
           */
          public boolean remove(Object o) { return map.remove(o) != null; }
  
          /**
           * @return an iterator over the keys of the backing map
           */
          public Iterator<K> iterator() {
              Node<K,V>[] t;
              ConcurrentHashMap<K,V> m = map;
              int f = (t = m.table) == null ? 0 : t.length;
              return new KeyIterator<K,V>(t, f, 0, f, m);
          }
  
          /**
           * Adds the specified key to this set view by mapping the key to
           * the default mapped value in the backing map, if defined.
           *
           * @param e key to be added
           * @return {@code true} if this set changed as a result of the call
           * @throws NullPointerException if the specified key is null
           * @throws UnsupportedOperationException if no default mapped value
           * for additions was provided
           */
          public boolean add(K e) {
              V v;
              if ((v = value) == null)
                  throw new UnsupportedOperationException();
              return map.putVal(e, v, true) == null;
          }
  
          /**
           * Adds all of the elements in the specified collection to this set,
           * as if by calling {@link #add} on each one.
           *
           * @param c the elements to be inserted into this set
           * @return {@code true} if this set changed as a result of the call
           * @throws NullPointerException if the collection or any of its
           * elements are {@code null}
           * @throws UnsupportedOperationException if no default mapped value
           * for additions was provided
           */
          public boolean addAll(Collection<? extends K> c) {
              boolean added = false;
              V v;
              if ((v = value) == null)
                  throw new UnsupportedOperationException();
              for (K e : c) {
                  if (map.putVal(e, v, true) == null)
                      added = true;
              }
              return added;
          }
  
          public int hashCode() {
              int h = 0;
              for (K e : this)
                  h += e.hashCode();
              return h;
          }
  
          public boolean equals(Object o) {
              Set<?> c;
              return ((o instanceof Set) &&
                      ((c = (Set<?>)o) == this ||
                       (containsAll(c) && c.containsAll(this))));
          }
  
          public Spliterator<K> spliterator() {
              Node<K,V>[] t;
              ConcurrentHashMap<K,V> m = map;
              long n = m.sumCount();
              int f = (t = m.table) == null ? 0 : t.length;
              return new KeySpliterator<K,V>(t, f, 0, f, n < 0L ? 0L : n);
          }
  
          public void forEach(Consumer<? super K> action) {
              if (action == null) throw new NullPointerException();
              Node<K,V>[] t;
              if ((t = map.table) != null) {
                  Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
                  for (Node<K,V> p; (p = it.advance()) != null; )
                      action.accept(p.key);
              }
          }
      }
  
      /**
       * A view of a ConcurrentHashMap as a {@link Collection} of
       * values, in which additions are disabled. This class cannot be
       * directly instantiated. See {@link #values()}.
       */
      static final class ValuesView<K,V> extends CollectionView<K,V,V>
          implements Collection<V>, Serializable {
          private static final long serialVersionUID = 2249069246763182397L;
          ValuesView(ConcurrentHashMap<K,V> map) { super(map); }
          public final boolean contains(Object o) {
              return map.containsValue(o);
          }
  
          public final boolean remove(Object o) {
              if (o != null) {
                  for (Iterator<V> it = iterator(); it.hasNext();) {
                      if (o.equals(it.next())) {
                          it.remove();
                          return true;
                      }
                  }
              }
              return false;
          }
  
          public final Iterator<V> iterator() {
              ConcurrentHashMap<K,V> m = map;
              Node<K,V>[] t;
              int f = (t = m.table) == null ? 0 : t.length;
              return new ValueIterator<K,V>(t, f, 0, f, m);
          }
  
          public final boolean add(V e) {
              throw new UnsupportedOperationException();
          }
          public final boolean addAll(Collection<? extends V> c) {
              throw new UnsupportedOperationException();
          }
  
          public boolean removeIf(Predicate<? super V> filter) {
              return map.removeValueIf(filter);
          }
  
          public Spliterator<V> spliterator() {
              Node<K,V>[] t;
              ConcurrentHashMap<K,V> m = map;
              long n = m.sumCount();
              int f = (t = m.table) == null ? 0 : t.length;
              return new ValueSpliterator<K,V>(t, f, 0, f, n < 0L ? 0L : n);
          }
  
          public void forEach(Consumer<? super V> action) {
              if (action == null) throw new NullPointerException();
              Node<K,V>[] t;
              if ((t = map.table) != null) {
                  Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
                  for (Node<K,V> p; (p = it.advance()) != null; )
                      action.accept(p.val);
              }
          }
      }
  
      /**
       * A view of a ConcurrentHashMap as a {@link Set} of (key, value)
       * entries.  This class cannot be directly instantiated. See
       * {@link #entrySet()}.
       */
      static final class EntrySetView<K,V> extends CollectionView<K,V, Entry<K,V>>
          implements Set<Entry<K,V>>, Serializable {
          private static final long serialVersionUID = 2249069246763182397L;
          EntrySetView(ConcurrentHashMap<K,V> map) { super(map); }
  
          public boolean contains(Object o) {
              Object k, v, r; Entry<?,?> e;
              return ((o instanceof Map.Entry) &&
                      (k = (e = (Entry<?,?>)o).getKey()) != null &&
                      (r = map.get(k)) != null &&
                      (v = e.getValue()) != null &&
                      (v == r || v.equals(r)));
          }
  
          public boolean remove(Object o) {
              Object k, v; Entry<?,?> e;
              return ((o instanceof Map.Entry) &&
                      (k = (e = (Entry<?,?>)o).getKey()) != null &&
                      (v = e.getValue()) != null &&
                      map.remove(k, v));
          }
  
          /**
           * @return an iterator over the entries of the backing map
           */
          public Iterator<Entry<K,V>> iterator() {
              ConcurrentHashMap<K,V> m = map;
              Node<K,V>[] t;
              int f = (t = m.table) == null ? 0 : t.length;
              return new EntryIterator<K,V>(t, f, 0, f, m);
          }
  
          public boolean add(Entry<K,V> e) {
              return map.putVal(e.getKey(), e.getValue(), false) == null;
          }
  
          public boolean addAll(Collection<? extends Entry<K,V>> c) {
              boolean added = false;
              for (Entry<K,V> e : c) {
                  if (add(e))
                      added = true;
              }
              return added;
          }
  
          public boolean removeIf(Predicate<? super Entry<K,V>> filter) {
              return map.removeEntryIf(filter);
          }
  
          public final int hashCode() {
              int h = 0;
              Node<K,V>[] t;
              if ((t = map.table) != null) {
                  Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
                  for (Node<K,V> p; (p = it.advance()) != null; ) {
                      h += p.hashCode();
                  }
              }
              return h;
          }
  
          public final boolean equals(Object o) {
              Set<?> c;
              return ((o instanceof Set) &&
                      ((c = (Set<?>)o) == this ||
                       (containsAll(c) && c.containsAll(this))));
          }
  
          public Spliterator<Entry<K,V>> spliterator() {
              Node<K,V>[] t;
              ConcurrentHashMap<K,V> m = map;
              long n = m.sumCount();
              int f = (t = m.table) == null ? 0 : t.length;
              return new EntrySpliterator<K,V>(t, f, 0, f, n < 0L ? 0L : n, m);
          }
  
          public void forEach(Consumer<? super Entry<K,V>> action) {
              if (action == null) throw new NullPointerException();
              Node<K,V>[] t;
              if ((t = map.table) != null) {
                  Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
                  for (Node<K,V> p; (p = it.advance()) != null; )
                      action.accept(new MapEntry<K,V>(p.key, p.val, map));
              }
          }
  
      }
  
      // -------------------------------------------------------
  
      /**
       * Base class for bulk tasks. Repeats some fields and code from
       * class Traverser, because we need to subclass CountedCompleter.
       */
      @SuppressWarnings("serial")
      abstract static class BulkTask<K,V,R> extends CountedCompleter<R> {
          Node<K,V>[] tab;        // same as Traverser
          Node<K,V> next;
          TableStack<K,V> stack, spare;
          int index;
          int baseIndex;
          int baseLimit;
          final int baseSize;
          int batch;              // split control
  
          BulkTask(BulkTask<K,V,?> par, int b, int i, int f, Node<K,V>[] t) {
              super(par);
              this.batch = b;
              this.index = this.baseIndex = i;
              if ((this.tab = t) == null)
                  this.baseSize = this.baseLimit = 0;
              else if (par == null)
                  this.baseSize = this.baseLimit = t.length;
              else {
                  this.baseLimit = f;
                  this.baseSize = par.baseSize;
              }
          }
  
          /**
           * Same as Traverser version.
           */
          final Node<K,V> advance() {
              Node<K,V> e;
              if ((e = next) != null)
                  e = e.next;
              for (;;) {
                  Node<K,V>[] t; int i, n;
                  if (e != null)
                      return next = e;
                  if (baseIndex >= baseLimit || (t = tab) == null ||
                      (n = t.length) <= (i = index) || i < 0)
                      return next = null;
                  if ((e = tabAt(t, i)) != null && e.hash < 0) {
                      if (e instanceof ForwardingNode) {
                          tab = ((ForwardingNode<K,V>)e).nextTable;
                          e = null;
                          pushState(t, i, n);
                          continue;
                      }
                      else if (e instanceof TreeBin)
                          e = ((TreeBin<K,V>)e).first;
                      else
                          e = null;
                  }
                  if (stack != null)
                      recoverState(n);
                  else if ((index = i + baseSize) >= n)
                      index = ++baseIndex;
              }
          }
  
          private void pushState(Node<K,V>[] t, int i, int n) {
              TableStack<K,V> s = spare;
              if (s != null)
                  spare = s.next;
              else
                  s = new TableStack<K,V>();
              s.tab = t;
              s.length = n;
              s.index = i;
              s.next = stack;
              stack = s;
          }
  
          private void recoverState(int n) {
              TableStack<K,V> s; int len;
              while ((s = stack) != null && (index += (len = s.length)) >= n) {
                  n = len;
                  index = s.index;
                  tab = s.tab;
                  s.tab = null;
                  TableStack<K,V> next = s.next;
                  s.next = spare; // save for reuse
                  stack = next;
                  spare = s;
              }
              if (s == null && (index += baseSize) >= n)
                  index = ++baseIndex;
          }
      }
  
      /*
       * Task classes. Coded in a regular but ugly format/style to
       * simplify checks that each variant differs in the right way from
       * others. The null screenings exist because compilers cannot tell
       * that we've already null-checked task arguments, so we force
       * simplest hoisted bypass to help avoid convoluted traps.
       */
      @SuppressWarnings("serial")
      static final class ForEachKeyTask<K,V>
          extends BulkTask<K,V,Void> {
          final Consumer<? super K> action;
          ForEachKeyTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               Consumer<? super K> action) {
              super(p, b, i, f, t);
              this.action = action;
          }
          public final void compute() {
              final Consumer<? super K> action;
              if ((action = this.action) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      new ForEachKeyTask<K,V>
                          (this, batch >>>= 1, baseLimit = h, f, tab,
                           action).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null;)
                      action.accept(p.key);
                  propagateCompletion();
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class ForEachValueTask<K,V>
          extends BulkTask<K,V,Void> {
          final Consumer<? super V> action;
          ForEachValueTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               Consumer<? super V> action) {
              super(p, b, i, f, t);
              this.action = action;
          }
          public final void compute() {
              final Consumer<? super V> action;
              if ((action = this.action) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      new ForEachValueTask<K,V>
                          (this, batch >>>= 1, baseLimit = h, f, tab,
                           action).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null;)
                      action.accept(p.val);
                  propagateCompletion();
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class ForEachEntryTask<K,V>
          extends BulkTask<K,V,Void> {
          final Consumer<? super Entry<K,V>> action;
          ForEachEntryTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               Consumer<? super Entry<K,V>> action) {
              super(p, b, i, f, t);
              this.action = action;
          }
          public final void compute() {
              final Consumer<? super Entry<K,V>> action;
              if ((action = this.action) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      new ForEachEntryTask<K,V>
                          (this, batch >>>= 1, baseLimit = h, f, tab,
                           action).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; )
                      action.accept(p);
                  propagateCompletion();
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class ForEachMappingTask<K,V>
          extends BulkTask<K,V,Void> {
          final BiConsumer<? super K, ? super V> action;
          ForEachMappingTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               BiConsumer<? super K,? super V> action) {
              super(p, b, i, f, t);
              this.action = action;
          }
          public final void compute() {
              final BiConsumer<? super K, ? super V> action;
              if ((action = this.action) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      new ForEachMappingTask<K,V>
                          (this, batch >>>= 1, baseLimit = h, f, tab,
                           action).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; )
                      action.accept(p.key, p.val);
                  propagateCompletion();
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class ForEachTransformedKeyTask<K,V,U>
          extends BulkTask<K,V,Void> {
          final Function<? super K, ? extends U> transformer;
          final Consumer<? super U> action;
          ForEachTransformedKeyTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               Function<? super K, ? extends U> transformer, Consumer<? super U> action) {
              super(p, b, i, f, t);
              this.transformer = transformer; this.action = action;
          }
          public final void compute() {
              final Function<? super K, ? extends U> transformer;
              final Consumer<? super U> action;
              if ((transformer = this.transformer) != null &&
                  (action = this.action) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      new ForEachTransformedKeyTask<K,V,U>
                          (this, batch >>>= 1, baseLimit = h, f, tab,
                           transformer, action).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; ) {
                      U u;
                      if ((u = transformer.apply(p.key)) != null)
                          action.accept(u);
                  }
                  propagateCompletion();
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class ForEachTransformedValueTask<K,V,U>
          extends BulkTask<K,V,Void> {
          final Function<? super V, ? extends U> transformer;
          final Consumer<? super U> action;
          ForEachTransformedValueTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               Function<? super V, ? extends U> transformer, Consumer<? super U> action) {
              super(p, b, i, f, t);
              this.transformer = transformer; this.action = action;
          }
          public final void compute() {
              final Function<? super V, ? extends U> transformer;
              final Consumer<? super U> action;
              if ((transformer = this.transformer) != null &&
                  (action = this.action) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      new ForEachTransformedValueTask<K,V,U>
                          (this, batch >>>= 1, baseLimit = h, f, tab,
                           transformer, action).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; ) {
                      U u;
                      if ((u = transformer.apply(p.val)) != null)
                          action.accept(u);
                  }
                  propagateCompletion();
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class ForEachTransformedEntryTask<K,V,U>
          extends BulkTask<K,V,Void> {
          final Function<Entry<K,V>, ? extends U> transformer;
          final Consumer<? super U> action;
          ForEachTransformedEntryTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               Function<Entry<K,V>, ? extends U> transformer, Consumer<? super U> action) {
              super(p, b, i, f, t);
              this.transformer = transformer; this.action = action;
          }
          public final void compute() {
              final Function<Entry<K,V>, ? extends U> transformer;
              final Consumer<? super U> action;
              if ((transformer = this.transformer) != null &&
                  (action = this.action) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      new ForEachTransformedEntryTask<K,V,U>
                          (this, batch >>>= 1, baseLimit = h, f, tab,
                           transformer, action).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; ) {
                      U u;
                      if ((u = transformer.apply(p)) != null)
                          action.accept(u);
                  }
                  propagateCompletion();
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class ForEachTransformedMappingTask<K,V,U>
          extends BulkTask<K,V,Void> {
          final BiFunction<? super K, ? super V, ? extends U> transformer;
          final Consumer<? super U> action;
          ForEachTransformedMappingTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               BiFunction<? super K, ? super V, ? extends U> transformer,
               Consumer<? super U> action) {
              super(p, b, i, f, t);
              this.transformer = transformer; this.action = action;
          }
          public final void compute() {
              final BiFunction<? super K, ? super V, ? extends U> transformer;
              final Consumer<? super U> action;
              if ((transformer = this.transformer) != null &&
                  (action = this.action) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      new ForEachTransformedMappingTask<K,V,U>
                          (this, batch >>>= 1, baseLimit = h, f, tab,
                           transformer, action).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; ) {
                      U u;
                      if ((u = transformer.apply(p.key, p.val)) != null)
                          action.accept(u);
                  }
                  propagateCompletion();
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class SearchKeysTask<K,V,U>
          extends BulkTask<K,V,U> {
          final Function<? super K, ? extends U> searchFunction;
          final AtomicReference<U> result;
          SearchKeysTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               Function<? super K, ? extends U> searchFunction,
               AtomicReference<U> result) {
              super(p, b, i, f, t);
              this.searchFunction = searchFunction; this.result = result;
          }
          public final U getRawResult() { return result.get(); }
          public final void compute() {
              final Function<? super K, ? extends U> searchFunction;
              final AtomicReference<U> result;
              if ((searchFunction = this.searchFunction) != null &&
                  (result = this.result) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      if (result.get() != null)
                          return;
                      addToPendingCount(1);
                      new SearchKeysTask<K,V,U>
                          (this, batch >>>= 1, baseLimit = h, f, tab,
                           searchFunction, result).fork();
                  }
                  while (result.get() == null) {
                      U u;
                      Node<K,V> p;
                      if ((p = advance()) == null) {
                          propagateCompletion();
                          break;
                      }
                      if ((u = searchFunction.apply(p.key)) != null) {
                          if (result.compareAndSet(null, u))
                              quietlyCompleteRoot();
                          break;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class SearchValuesTask<K,V,U>
          extends BulkTask<K,V,U> {
          final Function<? super V, ? extends U> searchFunction;
          final AtomicReference<U> result;
          SearchValuesTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               Function<? super V, ? extends U> searchFunction,
               AtomicReference<U> result) {
              super(p, b, i, f, t);
              this.searchFunction = searchFunction; this.result = result;
          }
          public final U getRawResult() { return result.get(); }
          public final void compute() {
              final Function<? super V, ? extends U> searchFunction;
              final AtomicReference<U> result;
              if ((searchFunction = this.searchFunction) != null &&
                  (result = this.result) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      if (result.get() != null)
                          return;
                      addToPendingCount(1);
                      new SearchValuesTask<K,V,U>
                          (this, batch >>>= 1, baseLimit = h, f, tab,
                           searchFunction, result).fork();
                  }
                  while (result.get() == null) {
                      U u;
                      Node<K,V> p;
                      if ((p = advance()) == null) {
                          propagateCompletion();
                          break;
                      }
                      if ((u = searchFunction.apply(p.val)) != null) {
                          if (result.compareAndSet(null, u))
                              quietlyCompleteRoot();
                          break;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class SearchEntriesTask<K,V,U>
          extends BulkTask<K,V,U> {
          final Function<Entry<K,V>, ? extends U> searchFunction;
          final AtomicReference<U> result;
          SearchEntriesTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               Function<Entry<K,V>, ? extends U> searchFunction,
               AtomicReference<U> result) {
              super(p, b, i, f, t);
              this.searchFunction = searchFunction; this.result = result;
          }
          public final U getRawResult() { return result.get(); }
          public final void compute() {
              final Function<Entry<K,V>, ? extends U> searchFunction;
              final AtomicReference<U> result;
              if ((searchFunction = this.searchFunction) != null &&
                  (result = this.result) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      if (result.get() != null)
                          return;
                      addToPendingCount(1);
                      new SearchEntriesTask<K,V,U>
                          (this, batch >>>= 1, baseLimit = h, f, tab,
                           searchFunction, result).fork();
                  }
                  while (result.get() == null) {
                      U u;
                      Node<K,V> p;
                      if ((p = advance()) == null) {
                          propagateCompletion();
                          break;
                      }
                      if ((u = searchFunction.apply(p)) != null) {
                          if (result.compareAndSet(null, u))
                              quietlyCompleteRoot();
                          return;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class SearchMappingsTask<K,V,U>
          extends BulkTask<K,V,U> {
          final BiFunction<? super K, ? super V, ? extends U> searchFunction;
          final AtomicReference<U> result;
          SearchMappingsTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               BiFunction<? super K, ? super V, ? extends U> searchFunction,
               AtomicReference<U> result) {
              super(p, b, i, f, t);
              this.searchFunction = searchFunction; this.result = result;
          }
          public final U getRawResult() { return result.get(); }
          public final void compute() {
              final BiFunction<? super K, ? super V, ? extends U> searchFunction;
              final AtomicReference<U> result;
              if ((searchFunction = this.searchFunction) != null &&
                  (result = this.result) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      if (result.get() != null)
                          return;
                      addToPendingCount(1);
                      new SearchMappingsTask<K,V,U>
                          (this, batch >>>= 1, baseLimit = h, f, tab,
                           searchFunction, result).fork();
                  }
                  while (result.get() == null) {
                      U u;
                      Node<K,V> p;
                      if ((p = advance()) == null) {
                          propagateCompletion();
                          break;
                      }
                      if ((u = searchFunction.apply(p.key, p.val)) != null) {
                          if (result.compareAndSet(null, u))
                              quietlyCompleteRoot();
                          break;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class ReduceKeysTask<K,V>
          extends BulkTask<K,V,K> {
          final BiFunction<? super K, ? super K, ? extends K> reducer;
          K result;
          ReduceKeysTask<K,V> rights, nextRight;
          ReduceKeysTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               ReduceKeysTask<K,V> nextRight,
               BiFunction<? super K, ? super K, ? extends K> reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.reducer = reducer;
          }
          public final K getRawResult() { return result; }
          public final void compute() {
              final BiFunction<? super K, ? super K, ? extends K> reducer;
              if ((reducer = this.reducer) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new ReduceKeysTask<K,V>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, reducer)).fork();
                  }
                  K r = null;
                  for (Node<K,V> p; (p = advance()) != null; ) {
                      K u = p.key;
                      r = (r == null) ? u : u == null ? r : reducer.apply(r, u);
                  }
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      ReduceKeysTask<K,V>
                          t = (ReduceKeysTask<K,V>)c,
                          s = t.rights;
                      while (s != null) {
                          K tr, sr;
                          if ((sr = s.result) != null)
                              t.result = (((tr = t.result) == null) ? sr :
                                          reducer.apply(tr, sr));
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class ReduceValuesTask<K,V>
          extends BulkTask<K,V,V> {
          final BiFunction<? super V, ? super V, ? extends V> reducer;
          V result;
          ReduceValuesTask<K,V> rights, nextRight;
          ReduceValuesTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               ReduceValuesTask<K,V> nextRight,
               BiFunction<? super V, ? super V, ? extends V> reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.reducer = reducer;
          }
          public final V getRawResult() { return result; }
          public final void compute() {
              final BiFunction<? super V, ? super V, ? extends V> reducer;
              if ((reducer = this.reducer) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new ReduceValuesTask<K,V>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, reducer)).fork();
                  }
                  V r = null;
                  for (Node<K,V> p; (p = advance()) != null; ) {
                      V v = p.val;
                      r = (r == null) ? v : reducer.apply(r, v);
                  }
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      ReduceValuesTask<K,V>
                          t = (ReduceValuesTask<K,V>)c,
                          s = t.rights;
                      while (s != null) {
                          V tr, sr;
                          if ((sr = s.result) != null)
                              t.result = (((tr = t.result) == null) ? sr :
                                          reducer.apply(tr, sr));
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class ReduceEntriesTask<K,V>
          extends BulkTask<K,V, Entry<K,V>> {
          final BiFunction<Entry<K,V>, Entry<K,V>, ? extends Entry<K,V>> reducer;
          Entry<K,V> result;
          ReduceEntriesTask<K,V> rights, nextRight;
          ReduceEntriesTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               ReduceEntriesTask<K,V> nextRight,
               BiFunction<Entry<K,V>, Entry<K,V>, ? extends Entry<K,V>> reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.reducer = reducer;
          }
          public final Entry<K,V> getRawResult() { return result; }
          public final void compute() {
              final BiFunction<Entry<K,V>, Entry<K,V>, ? extends Entry<K,V>> reducer;
              if ((reducer = this.reducer) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new ReduceEntriesTask<K,V>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, reducer)).fork();
                  }
                  Entry<K,V> r = null;
                  for (Node<K,V> p; (p = advance()) != null; )
                      r = (r == null) ? p : reducer.apply(r, p);
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      ReduceEntriesTask<K,V>
                          t = (ReduceEntriesTask<K,V>)c,
                          s = t.rights;
                      while (s != null) {
                          Entry<K,V> tr, sr;
                          if ((sr = s.result) != null)
                              t.result = (((tr = t.result) == null) ? sr :
                                          reducer.apply(tr, sr));
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class MapReduceKeysTask<K,V,U>
          extends BulkTask<K,V,U> {
          final Function<? super K, ? extends U> transformer;
          final BiFunction<? super U, ? super U, ? extends U> reducer;
          U result;
          MapReduceKeysTask<K,V,U> rights, nextRight;
          MapReduceKeysTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               MapReduceKeysTask<K,V,U> nextRight,
               Function<? super K, ? extends U> transformer,
               BiFunction<? super U, ? super U, ? extends U> reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.transformer = transformer;
              this.reducer = reducer;
          }
          public final U getRawResult() { return result; }
          public final void compute() {
              final Function<? super K, ? extends U> transformer;
              final BiFunction<? super U, ? super U, ? extends U> reducer;
              if ((transformer = this.transformer) != null &&
                  (reducer = this.reducer) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new MapReduceKeysTask<K,V,U>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, transformer, reducer)).fork();
                  }
                  U r = null;
                  for (Node<K,V> p; (p = advance()) != null; ) {
                      U u;
                      if ((u = transformer.apply(p.key)) != null)
                          r = (r == null) ? u : reducer.apply(r, u);
                  }
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      MapReduceKeysTask<K,V,U>
                          t = (MapReduceKeysTask<K,V,U>)c,
                          s = t.rights;
                      while (s != null) {
                          U tr, sr;
                          if ((sr = s.result) != null)
                              t.result = (((tr = t.result) == null) ? sr :
                                          reducer.apply(tr, sr));
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class MapReduceValuesTask<K,V,U>
          extends BulkTask<K,V,U> {
          final Function<? super V, ? extends U> transformer;
          final BiFunction<? super U, ? super U, ? extends U> reducer;
          U result;
          MapReduceValuesTask<K,V,U> rights, nextRight;
          MapReduceValuesTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               MapReduceValuesTask<K,V,U> nextRight,
               Function<? super V, ? extends U> transformer,
               BiFunction<? super U, ? super U, ? extends U> reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.transformer = transformer;
              this.reducer = reducer;
          }
          public final U getRawResult() { return result; }
          public final void compute() {
              final Function<? super V, ? extends U> transformer;
              final BiFunction<? super U, ? super U, ? extends U> reducer;
              if ((transformer = this.transformer) != null &&
                  (reducer = this.reducer) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new MapReduceValuesTask<K,V,U>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, transformer, reducer)).fork();
                  }
                  U r = null;
                  for (Node<K,V> p; (p = advance()) != null; ) {
                      U u;
                      if ((u = transformer.apply(p.val)) != null)
                          r = (r == null) ? u : reducer.apply(r, u);
                  }
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      MapReduceValuesTask<K,V,U>
                          t = (MapReduceValuesTask<K,V,U>)c,
                          s = t.rights;
                      while (s != null) {
                          U tr, sr;
                          if ((sr = s.result) != null)
                              t.result = (((tr = t.result) == null) ? sr :
                                          reducer.apply(tr, sr));
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class MapReduceEntriesTask<K,V,U>
          extends BulkTask<K,V,U> {
          final Function<Entry<K,V>, ? extends U> transformer;
          final BiFunction<? super U, ? super U, ? extends U> reducer;
          U result;
          MapReduceEntriesTask<K,V,U> rights, nextRight;
          MapReduceEntriesTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               MapReduceEntriesTask<K,V,U> nextRight,
               Function<Entry<K,V>, ? extends U> transformer,
               BiFunction<? super U, ? super U, ? extends U> reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.transformer = transformer;
              this.reducer = reducer;
          }
          public final U getRawResult() { return result; }
          public final void compute() {
              final Function<Entry<K,V>, ? extends U> transformer;
              final BiFunction<? super U, ? super U, ? extends U> reducer;
              if ((transformer = this.transformer) != null &&
                  (reducer = this.reducer) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new MapReduceEntriesTask<K,V,U>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, transformer, reducer)).fork();
                  }
                  U r = null;
                  for (Node<K,V> p; (p = advance()) != null; ) {
                      U u;
                      if ((u = transformer.apply(p)) != null)
                          r = (r == null) ? u : reducer.apply(r, u);
                  }
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      MapReduceEntriesTask<K,V,U>
                          t = (MapReduceEntriesTask<K,V,U>)c,
                          s = t.rights;
                      while (s != null) {
                          U tr, sr;
                          if ((sr = s.result) != null)
                              t.result = (((tr = t.result) == null) ? sr :
                                          reducer.apply(tr, sr));
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class MapReduceMappingsTask<K,V,U>
          extends BulkTask<K,V,U> {
          final BiFunction<? super K, ? super V, ? extends U> transformer;
          final BiFunction<? super U, ? super U, ? extends U> reducer;
          U result;
          MapReduceMappingsTask<K,V,U> rights, nextRight;
          MapReduceMappingsTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               MapReduceMappingsTask<K,V,U> nextRight,
               BiFunction<? super K, ? super V, ? extends U> transformer,
               BiFunction<? super U, ? super U, ? extends U> reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.transformer = transformer;
              this.reducer = reducer;
          }
          public final U getRawResult() { return result; }
          public final void compute() {
              final BiFunction<? super K, ? super V, ? extends U> transformer;
              final BiFunction<? super U, ? super U, ? extends U> reducer;
              if ((transformer = this.transformer) != null &&
                  (reducer = this.reducer) != null) {
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new MapReduceMappingsTask<K,V,U>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, transformer, reducer)).fork();
                  }
                  U r = null;
                  for (Node<K,V> p; (p = advance()) != null; ) {
                      U u;
                      if ((u = transformer.apply(p.key, p.val)) != null)
                          r = (r == null) ? u : reducer.apply(r, u);
                  }
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      MapReduceMappingsTask<K,V,U>
                          t = (MapReduceMappingsTask<K,V,U>)c,
                          s = t.rights;
                      while (s != null) {
                          U tr, sr;
                          if ((sr = s.result) != null)
                              t.result = (((tr = t.result) == null) ? sr :
                                          reducer.apply(tr, sr));
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class MapReduceKeysToDoubleTask<K,V>
          extends BulkTask<K,V,Double> {
          final ToDoubleFunction<? super K> transformer;
          final DoubleBinaryOperator reducer;
          final double basis;
          double result;
          MapReduceKeysToDoubleTask<K,V> rights, nextRight;
          MapReduceKeysToDoubleTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               MapReduceKeysToDoubleTask<K,V> nextRight,
               ToDoubleFunction<? super K> transformer,
               double basis,
               DoubleBinaryOperator reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.transformer = transformer;
              this.basis = basis; this.reducer = reducer;
          }
          public final Double getRawResult() { return result; }
          public final void compute() {
              final ToDoubleFunction<? super K> transformer;
              final DoubleBinaryOperator reducer;
              if ((transformer = this.transformer) != null &&
                  (reducer = this.reducer) != null) {
                  double r = this.basis;
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new MapReduceKeysToDoubleTask<K,V>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, transformer, r, reducer)).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; )
                      r = reducer.applyAsDouble(r, transformer.applyAsDouble(p.key));
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      MapReduceKeysToDoubleTask<K,V>
                          t = (MapReduceKeysToDoubleTask<K,V>)c,
                          s = t.rights;
                      while (s != null) {
                          t.result = reducer.applyAsDouble(t.result, s.result);
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class MapReduceValuesToDoubleTask<K,V>
          extends BulkTask<K,V,Double> {
          final ToDoubleFunction<? super V> transformer;
          final DoubleBinaryOperator reducer;
          final double basis;
          double result;
          MapReduceValuesToDoubleTask<K,V> rights, nextRight;
          MapReduceValuesToDoubleTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               MapReduceValuesToDoubleTask<K,V> nextRight,
               ToDoubleFunction<? super V> transformer,
               double basis,
               DoubleBinaryOperator reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.transformer = transformer;
              this.basis = basis; this.reducer = reducer;
          }
          public final Double getRawResult() { return result; }
          public final void compute() {
              final ToDoubleFunction<? super V> transformer;
              final DoubleBinaryOperator reducer;
              if ((transformer = this.transformer) != null &&
                  (reducer = this.reducer) != null) {
                  double r = this.basis;
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new MapReduceValuesToDoubleTask<K,V>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, transformer, r, reducer)).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; )
                      r = reducer.applyAsDouble(r, transformer.applyAsDouble(p.val));
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      MapReduceValuesToDoubleTask<K,V>
                          t = (MapReduceValuesToDoubleTask<K,V>)c,
                          s = t.rights;
                      while (s != null) {
                          t.result = reducer.applyAsDouble(t.result, s.result);
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class MapReduceEntriesToDoubleTask<K,V>
          extends BulkTask<K,V,Double> {
          final ToDoubleFunction<Entry<K,V>> transformer;
          final DoubleBinaryOperator reducer;
          final double basis;
          double result;
          MapReduceEntriesToDoubleTask<K,V> rights, nextRight;
          MapReduceEntriesToDoubleTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               MapReduceEntriesToDoubleTask<K,V> nextRight,
               ToDoubleFunction<Entry<K,V>> transformer,
               double basis,
               DoubleBinaryOperator reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.transformer = transformer;
              this.basis = basis; this.reducer = reducer;
          }
          public final Double getRawResult() { return result; }
          public final void compute() {
              final ToDoubleFunction<Entry<K,V>> transformer;
              final DoubleBinaryOperator reducer;
              if ((transformer = this.transformer) != null &&
                  (reducer = this.reducer) != null) {
                  double r = this.basis;
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new MapReduceEntriesToDoubleTask<K,V>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, transformer, r, reducer)).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; )
                      r = reducer.applyAsDouble(r, transformer.applyAsDouble(p));
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      MapReduceEntriesToDoubleTask<K,V>
                          t = (MapReduceEntriesToDoubleTask<K,V>)c,
                          s = t.rights;
                      while (s != null) {
                          t.result = reducer.applyAsDouble(t.result, s.result);
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class MapReduceMappingsToDoubleTask<K,V>
          extends BulkTask<K,V,Double> {
          final ToDoubleBiFunction<? super K, ? super V> transformer;
          final DoubleBinaryOperator reducer;
          final double basis;
          double result;
          MapReduceMappingsToDoubleTask<K,V> rights, nextRight;
          MapReduceMappingsToDoubleTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               MapReduceMappingsToDoubleTask<K,V> nextRight,
               ToDoubleBiFunction<? super K, ? super V> transformer,
               double basis,
               DoubleBinaryOperator reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.transformer = transformer;
              this.basis = basis; this.reducer = reducer;
          }
          public final Double getRawResult() { return result; }
          public final void compute() {
              final ToDoubleBiFunction<? super K, ? super V> transformer;
              final DoubleBinaryOperator reducer;
              if ((transformer = this.transformer) != null &&
                  (reducer = this.reducer) != null) {
                  double r = this.basis;
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new MapReduceMappingsToDoubleTask<K,V>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, transformer, r, reducer)).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; )
                      r = reducer.applyAsDouble(r, transformer.applyAsDouble(p.key, p.val));
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      MapReduceMappingsToDoubleTask<K,V>
                          t = (MapReduceMappingsToDoubleTask<K,V>)c,
                          s = t.rights;
                      while (s != null) {
                          t.result = reducer.applyAsDouble(t.result, s.result);
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class MapReduceKeysToLongTask<K,V>
          extends BulkTask<K,V,Long> {
          final ToLongFunction<? super K> transformer;
          final LongBinaryOperator reducer;
          final long basis;
          long result;
          MapReduceKeysToLongTask<K,V> rights, nextRight;
          MapReduceKeysToLongTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               MapReduceKeysToLongTask<K,V> nextRight,
               ToLongFunction<? super K> transformer,
               long basis,
               LongBinaryOperator reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.transformer = transformer;
              this.basis = basis; this.reducer = reducer;
          }
          public final Long getRawResult() { return result; }
          public final void compute() {
              final ToLongFunction<? super K> transformer;
              final LongBinaryOperator reducer;
              if ((transformer = this.transformer) != null &&
                  (reducer = this.reducer) != null) {
                  long r = this.basis;
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new MapReduceKeysToLongTask<K,V>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, transformer, r, reducer)).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; )
                      r = reducer.applyAsLong(r, transformer.applyAsLong(p.key));
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      MapReduceKeysToLongTask<K,V>
                          t = (MapReduceKeysToLongTask<K,V>)c,
                          s = t.rights;
                      while (s != null) {
                          t.result = reducer.applyAsLong(t.result, s.result);
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class MapReduceValuesToLongTask<K,V>
          extends BulkTask<K,V,Long> {
          final ToLongFunction<? super V> transformer;
          final LongBinaryOperator reducer;
          final long basis;
          long result;
          MapReduceValuesToLongTask<K,V> rights, nextRight;
          MapReduceValuesToLongTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               MapReduceValuesToLongTask<K,V> nextRight,
               ToLongFunction<? super V> transformer,
               long basis,
               LongBinaryOperator reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.transformer = transformer;
              this.basis = basis; this.reducer = reducer;
          }
          public final Long getRawResult() { return result; }
          public final void compute() {
              final ToLongFunction<? super V> transformer;
              final LongBinaryOperator reducer;
              if ((transformer = this.transformer) != null &&
                  (reducer = this.reducer) != null) {
                  long r = this.basis;
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new MapReduceValuesToLongTask<K,V>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, transformer, r, reducer)).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; )
                      r = reducer.applyAsLong(r, transformer.applyAsLong(p.val));
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      MapReduceValuesToLongTask<K,V>
                          t = (MapReduceValuesToLongTask<K,V>)c,
                          s = t.rights;
                      while (s != null) {
                          t.result = reducer.applyAsLong(t.result, s.result);
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class MapReduceEntriesToLongTask<K,V>
          extends BulkTask<K,V,Long> {
          final ToLongFunction<Entry<K,V>> transformer;
          final LongBinaryOperator reducer;
          final long basis;
          long result;
          MapReduceEntriesToLongTask<K,V> rights, nextRight;
          MapReduceEntriesToLongTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               MapReduceEntriesToLongTask<K,V> nextRight,
               ToLongFunction<Entry<K,V>> transformer,
               long basis,
               LongBinaryOperator reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.transformer = transformer;
              this.basis = basis; this.reducer = reducer;
          }
          public final Long getRawResult() { return result; }
          public final void compute() {
              final ToLongFunction<Entry<K,V>> transformer;
              final LongBinaryOperator reducer;
              if ((transformer = this.transformer) != null &&
                  (reducer = this.reducer) != null) {
                  long r = this.basis;
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new MapReduceEntriesToLongTask<K,V>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, transformer, r, reducer)).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; )
                      r = reducer.applyAsLong(r, transformer.applyAsLong(p));
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      MapReduceEntriesToLongTask<K,V>
                          t = (MapReduceEntriesToLongTask<K,V>)c,
                          s = t.rights;
                      while (s != null) {
                          t.result = reducer.applyAsLong(t.result, s.result);
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class MapReduceMappingsToLongTask<K,V>
          extends BulkTask<K,V,Long> {
          final ToLongBiFunction<? super K, ? super V> transformer;
          final LongBinaryOperator reducer;
          final long basis;
          long result;
          MapReduceMappingsToLongTask<K,V> rights, nextRight;
          MapReduceMappingsToLongTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               MapReduceMappingsToLongTask<K,V> nextRight,
               ToLongBiFunction<? super K, ? super V> transformer,
               long basis,
               LongBinaryOperator reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.transformer = transformer;
              this.basis = basis; this.reducer = reducer;
          }
          public final Long getRawResult() { return result; }
          public final void compute() {
              final ToLongBiFunction<? super K, ? super V> transformer;
              final LongBinaryOperator reducer;
              if ((transformer = this.transformer) != null &&
                  (reducer = this.reducer) != null) {
                  long r = this.basis;
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new MapReduceMappingsToLongTask<K,V>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, transformer, r, reducer)).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; )
                      r = reducer.applyAsLong(r, transformer.applyAsLong(p.key, p.val));
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      MapReduceMappingsToLongTask<K,V>
                          t = (MapReduceMappingsToLongTask<K,V>)c,
                          s = t.rights;
                      while (s != null) {
                          t.result = reducer.applyAsLong(t.result, s.result);
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class MapReduceKeysToIntTask<K,V>
          extends BulkTask<K,V,Integer> {
          final ToIntFunction<? super K> transformer;
          final IntBinaryOperator reducer;
          final int basis;
          int result;
          MapReduceKeysToIntTask<K,V> rights, nextRight;
          MapReduceKeysToIntTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               MapReduceKeysToIntTask<K,V> nextRight,
               ToIntFunction<? super K> transformer,
               int basis,
               IntBinaryOperator reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.transformer = transformer;
              this.basis = basis; this.reducer = reducer;
          }
          public final Integer getRawResult() { return result; }
          public final void compute() {
              final ToIntFunction<? super K> transformer;
              final IntBinaryOperator reducer;
              if ((transformer = this.transformer) != null &&
                  (reducer = this.reducer) != null) {
                  int r = this.basis;
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new MapReduceKeysToIntTask<K,V>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, transformer, r, reducer)).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; )
                      r = reducer.applyAsInt(r, transformer.applyAsInt(p.key));
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      MapReduceKeysToIntTask<K,V>
                          t = (MapReduceKeysToIntTask<K,V>)c,
                          s = t.rights;
                      while (s != null) {
                          t.result = reducer.applyAsInt(t.result, s.result);
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class MapReduceValuesToIntTask<K,V>
          extends BulkTask<K,V,Integer> {
          final ToIntFunction<? super V> transformer;
          final IntBinaryOperator reducer;
          final int basis;
          int result;
          MapReduceValuesToIntTask<K,V> rights, nextRight;
          MapReduceValuesToIntTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               MapReduceValuesToIntTask<K,V> nextRight,
               ToIntFunction<? super V> transformer,
               int basis,
               IntBinaryOperator reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.transformer = transformer;
              this.basis = basis; this.reducer = reducer;
          }
          public final Integer getRawResult() { return result; }
          public final void compute() {
              final ToIntFunction<? super V> transformer;
              final IntBinaryOperator reducer;
              if ((transformer = this.transformer) != null &&
                  (reducer = this.reducer) != null) {
                  int r = this.basis;
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new MapReduceValuesToIntTask<K,V>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, transformer, r, reducer)).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; )
                      r = reducer.applyAsInt(r, transformer.applyAsInt(p.val));
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      MapReduceValuesToIntTask<K,V>
                          t = (MapReduceValuesToIntTask<K,V>)c,
                          s = t.rights;
                      while (s != null) {
                          t.result = reducer.applyAsInt(t.result, s.result);
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class MapReduceEntriesToIntTask<K,V>
          extends BulkTask<K,V,Integer> {
          final ToIntFunction<Entry<K,V>> transformer;
          final IntBinaryOperator reducer;
          final int basis;
          int result;
          MapReduceEntriesToIntTask<K,V> rights, nextRight;
          MapReduceEntriesToIntTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               MapReduceEntriesToIntTask<K,V> nextRight,
               ToIntFunction<Entry<K,V>> transformer,
               int basis,
               IntBinaryOperator reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.transformer = transformer;
              this.basis = basis; this.reducer = reducer;
          }
          public final Integer getRawResult() { return result; }
          public final void compute() {
              final ToIntFunction<Entry<K,V>> transformer;
              final IntBinaryOperator reducer;
              if ((transformer = this.transformer) != null &&
                  (reducer = this.reducer) != null) {
                  int r = this.basis;
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new MapReduceEntriesToIntTask<K,V>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, transformer, r, reducer)).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; )
                      r = reducer.applyAsInt(r, transformer.applyAsInt(p));
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      MapReduceEntriesToIntTask<K,V>
                          t = (MapReduceEntriesToIntTask<K,V>)c,
                          s = t.rights;
                      while (s != null) {
                          t.result = reducer.applyAsInt(t.result, s.result);
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      @SuppressWarnings("serial")
      static final class MapReduceMappingsToIntTask<K,V>
          extends BulkTask<K,V,Integer> {
          final ToIntBiFunction<? super K, ? super V> transformer;
          final IntBinaryOperator reducer;
          final int basis;
          int result;
          MapReduceMappingsToIntTask<K,V> rights, nextRight;
          MapReduceMappingsToIntTask
              (BulkTask<K,V,?> p, int b, int i, int f, Node<K,V>[] t,
               MapReduceMappingsToIntTask<K,V> nextRight,
               ToIntBiFunction<? super K, ? super V> transformer,
               int basis,
               IntBinaryOperator reducer) {
              super(p, b, i, f, t); this.nextRight = nextRight;
              this.transformer = transformer;
              this.basis = basis; this.reducer = reducer;
          }
          public final Integer getRawResult() { return result; }
          public final void compute() {
              final ToIntBiFunction<? super K, ? super V> transformer;
              final IntBinaryOperator reducer;
              if ((transformer = this.transformer) != null &&
                  (reducer = this.reducer) != null) {
                  int r = this.basis;
                  for (int i = baseIndex, f, h; batch > 0 &&
                           (h = ((f = baseLimit) + i) >>> 1) > i;) {
                      addToPendingCount(1);
                      (rights = new MapReduceMappingsToIntTask<K,V>
                       (this, batch >>>= 1, baseLimit = h, f, tab,
                        rights, transformer, r, reducer)).fork();
                  }
                  for (Node<K,V> p; (p = advance()) != null; )
                      r = reducer.applyAsInt(r, transformer.applyAsInt(p.key, p.val));
                  result = r;
                  CountedCompleter<?> c;
                  for (c = firstComplete(); c != null; c = c.nextComplete()) {
                      @SuppressWarnings("unchecked")
                      MapReduceMappingsToIntTask<K,V>
                          t = (MapReduceMappingsToIntTask<K,V>)c,
                          s = t.rights;
                      while (s != null) {
                          t.result = reducer.applyAsInt(t.result, s.result);
                          s = t.rights = s.nextRight;
                      }
                  }
              }
          }
      }
  
      // Unsafe mechanics
      private static final sun.misc.Unsafe U = sun.misc.Unsafe.getUnsafe();
      private static final long SIZECTL;
      private static final long TRANSFERINDEX;
      private static final long BASECOUNT;
      private static final long CELLSBUSY;
      private static final long CELLVALUE;
      private static final int ABASE;
      private static final int ASHIFT;
  
      static {
          try {
              SIZECTL = U.objectFieldOffset
                  (ConcurrentHashMap.class.getDeclaredField("sizeCtl"));
              TRANSFERINDEX = U.objectFieldOffset
                  (ConcurrentHashMap.class.getDeclaredField("transferIndex"));
              BASECOUNT = U.objectFieldOffset
                  (ConcurrentHashMap.class.getDeclaredField("baseCount"));
              CELLSBUSY = U.objectFieldOffset
                  (ConcurrentHashMap.class.getDeclaredField("cellsBusy"));
  
              CELLVALUE = U.objectFieldOffset
                  (CounterCell.class.getDeclaredField("value"));
  
              ABASE = U.arrayBaseOffset(Node[].class);
              int scale = U.arrayIndexScale(Node[].class);
              if ((scale & (scale - 1)) != 0)
                  throw new Error("array index scale not a power of two");
              ASHIFT = 31 - Integer.numberOfLeadingZeros(scale);
          } catch (ReflectiveOperationException e) {
              throw new Error(e);
          }
  
          // Reduce the risk of rare disastrous classloading in first call to
          // LockSupport.park: https://bugs.openjdk.java.net/browse/JDK-8074773
          Class<?> ensureLoaded = LockSupport.class;
      }
  }
  