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.util.AbstractSet;
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.Objects;
  import java.util.Set;
  import java.util.Spliterator;
  import java.util.Spliterators;
  import java.util.function.Consumer;
  import java.util.function.Predicate;
  
  // BEGIN android-note
  // removed link to collections framework docs
  // fixed framework docs link to "Collection#optional"
  // END android-note
  
  /**
   * A {@link Set} that uses an internal {@link CopyOnWriteArrayList}
   * for all of its operations.  Thus, it shares the same basic properties:
   * <ul>
   *  <li>It is best suited for applications in which set sizes generally
   *       stay small, read-only operations
   *       vastly outnumber mutative operations, and you need
   *       to prevent interference among threads during traversal.
   *  <li>It is thread-safe.
   *  <li>Mutative operations ({@code add}, {@code set}, {@code remove}, etc.)
   *      are expensive since they usually entail copying the entire underlying
   *      array.
   *  <li>Iterators do not support the mutative {@code remove} operation.
   *  <li>Traversal via iterators is fast and cannot encounter
   *      interference from other threads. Iterators rely on
   *      unchanging snapshots of the array at the time the iterators were
   *      constructed.
   * </ul>
   *
   * <p><b>Sample Usage.</b> The following code sketch uses a
   * copy-on-write set to maintain a set of Handler objects that
   * perform some action upon state updates.
   *
   * <pre> {@code
   * class Handler { void handle(); ... }
   *
   * class X {
   *   private final CopyOnWriteArraySet<Handler> handlers
   *     = new CopyOnWriteArraySet<>();
   *   public void addHandler(Handler h) { handlers.add(h); }
   *
   *   private long internalState;
   *   private synchronized void changeState() { internalState = ...; }
   *
   *   public void update() {
   *     changeState();
   *     for (Handler handler : handlers)
   *       handler.handle();
   *   }
   * }}</pre>
   *
   * @see CopyOnWriteArrayList
   * @since 1.5
   * @author Doug Lea
   * @param <E> the type of elements held in this set
   */
  public class CopyOnWriteArraySet<E> extends AbstractSet<E>
          implements java.io.Serializable {
      private static final long serialVersionUID = 5457747651344034263L;
  
      private final CopyOnWriteArrayList<E> al;
  
      /**
       * Creates an empty set.
       */
      public CopyOnWriteArraySet() {
          al = new CopyOnWriteArrayList<E>();
      }
  
      /**
       * Creates a set containing all of the elements of the specified
       * collection.
       *
       * @param c the collection of elements to initially contain
       * @throws NullPointerException if the specified collection is null
       */
      public CopyOnWriteArraySet(Collection<? extends E> c) {
          if (c.getClass() == CopyOnWriteArraySet.class) {
              @SuppressWarnings("unchecked") CopyOnWriteArraySet<E> cc =
                  (CopyOnWriteArraySet<E>)c;
              al = new CopyOnWriteArrayList<E>(cc.al);
          }
          else {
              al = new CopyOnWriteArrayList<E>();
              al.addAllAbsent(c);
          }
      }
  
      /**
       * Returns the number of elements in this set.
       *
       * @return the number of elements in this set
       */
      public int size() {
          return al.size();
      }
  
      /**
       * Returns {@code true} if this set contains no elements.
       *
       * @return {@code true} if this set contains no elements
       */
      public boolean isEmpty() {
          return al.isEmpty();
      }
  
      /**
       * Returns {@code true} if this set contains the specified element.
       * More formally, returns {@code true} if and only if this set
       * contains an element {@code e} such that {@code Objects.equals(o, e)}.
       *
       * @param o element whose presence in this set is to be tested
       * @return {@code true} if this set contains the specified element
       */
      public boolean contains(Object o) {
          return al.contains(o);
      }
  
      /**
       * Returns an array containing all of the elements in this set.
       * If this set makes any guarantees as to what order its elements
       * are returned by its iterator, this method must return the
       * elements in the same order.
       *
       * <p>The returned array will be "safe" in that no references to it
       * are maintained by this set.  (In other words, this method must
       * allocate a new array even if this set is backed by an array).
       * The caller is thus free to modify the returned array.
       *
       * <p>This method acts as bridge between array-based and collection-based
       * APIs.
       *
       * @return an array containing all the elements in this set
       */
      public Object[] toArray() {
          return al.toArray();
      }
  
      /**
       * Returns an array containing all of the elements in this set; the
       * runtime type of the returned array is that of the specified array.
       * If the set fits in the specified array, it is returned therein.
       * Otherwise, a new array is allocated with the runtime type of the
       * specified array and the size of this set.
       *
       * <p>If this set fits in the specified array with room to spare
       * (i.e., the array has more elements than this set), the element in
       * the array immediately following the end of the set is set to
       * {@code null}.  (This is useful in determining the length of this
       * set <i>only</i> if the caller knows that this set does not contain
       * any null elements.)
       *
       * <p>If this set makes any guarantees as to what order its elements
       * are returned by its iterator, this method must return the elements
       * in the same order.
       *
       * <p>Like the {@link #toArray()} method, this method acts as bridge between
       * array-based and collection-based APIs.  Further, this method allows
       * precise control over the runtime type of the output array, and may,
       * under certain circumstances, be used to save allocation costs.
       *
       * <p>Suppose {@code x} is a set known to contain only strings.
       * The following code can be used to dump the set into a newly allocated
       * array of {@code String}:
       *
       * <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
       *
       * Note that {@code toArray(new Object[0])} is identical in function to
       * {@code toArray()}.
       *
       * @param a the array into which the elements of this set are to be
       *        stored, if it is big enough; otherwise, a new array of the same
       *        runtime type is allocated for this purpose.
       * @return an array containing all the elements in this set
       * @throws ArrayStoreException if the runtime type of the specified array
       *         is not a supertype of the runtime type of every element in this
       *         set
       * @throws NullPointerException if the specified array is null
       */
      public <T> T[] toArray(T[] a) {
          return al.toArray(a);
      }
  
      /**
       * Removes all of the elements from this set.
       * The set will be empty after this call returns.
       */
      public void clear() {
          al.clear();
      }
  
      /**
       * Removes the specified element from this set if it is present.
       * More formally, removes an element {@code e} such that
       * {@code Objects.equals(o, e)}, if this set contains such an element.
       * Returns {@code true} if this set contained the element (or
       * equivalently, if this set changed as a result of the call).
       * (This set will not contain the element once the call returns.)
       *
       * @param o object to be removed from this set, if present
       * @return {@code true} if this set contained the specified element
       */
      public boolean remove(Object o) {
          return al.remove(o);
      }
  
      /**
       * Adds the specified element to this set if it is not already present.
       * More formally, adds the specified element {@code e} to this set if
       * the set contains no element {@code e2} such that
       * {@code Objects.equals(e, e2)}.
       * If this set already contains the element, the call leaves the set
       * unchanged and returns {@code false}.
       *
       * @param e element to be added to this set
       * @return {@code true} if this set did not already contain the specified
       *         element
       */
      public boolean add(E e) {
          return al.addIfAbsent(e);
      }
  
      /**
       * Returns {@code true} if this set contains all of the elements of the
       * specified collection.  If the specified collection is also a set, this
       * method returns {@code true} if it is a <i>subset</i> of this set.
       *
       * @param  c collection to be checked for containment in this set
       * @return {@code true} if this set contains all of the elements of the
       *         specified collection
       * @throws NullPointerException if the specified collection is null
       * @see #contains(Object)
       */
      public boolean containsAll(Collection<?> c) {
          return (c instanceof Set)
              ? compareSets(al.getArray(), (Set<?>) c) >= 0
              : al.containsAll(c);
      }
  
      /**
       * Tells whether the objects in snapshot (regarded as a set) are a
       * superset of the given set.
       *
       * @return -1 if snapshot is not a superset, 0 if the two sets
       * contain precisely the same elements, and 1 if snapshot is a
       * proper superset of the given set
       */
      private static int compareSets(Object[] snapshot, Set<?> set) {
          // Uses O(n^2) algorithm, that is only appropriate for small
          // sets, which CopyOnWriteArraySets should be.
          //
          // Optimize up to O(n) if the two sets share a long common prefix,
          // as might happen if one set was created as a copy of the other set.
  
          final int len = snapshot.length;
          // Mark matched elements to avoid re-checking
          final boolean[] matched = new boolean[len];
  
          // j is the largest int with matched[i] true for { i | 0 <= i < j }
          int j = 0;
          outer: for (Object x : set) {
              for (int i = j; i < len; i++) {
                  if (!matched[i] && Objects.equals(x, snapshot[i])) {
                      matched[i] = true;
                      if (i == j)
                          do { j++; } while (j < len && matched[j]);
                      continue outer;
                  }
              }
              return -1;
          }
          return (j == len) ? 0 : 1;
      }
  
      /**
       * Adds all of the elements in the specified collection to this set if
       * they're not already present.  If the specified collection is also a
       * set, the {@code addAll} operation effectively modifies this set so
       * that its value is the <i>union</i> of the two sets.  The behavior of
       * this operation is undefined if the specified collection is modified
       * while the operation is in progress.
       *
       * @param  c collection containing elements to be added to this set
       * @return {@code true} if this set changed as a result of the call
       * @throws NullPointerException if the specified collection is null
       * @see #add(Object)
       */
      public boolean addAll(Collection<? extends E> c) {
          return al.addAllAbsent(c) > 0;
      }
  
      /**
       * Removes from this set all of its elements that are contained in the
       * specified collection.  If the specified collection is also a set,
       * this operation effectively modifies this set so that its value is the
       * <i>asymmetric set difference</i> of the two sets.
       *
       * @param  c collection containing elements to be removed from this set
       * @return {@code true} if this set changed as a result of the call
       * @throws ClassCastException if the class of an element of this set
       *         is incompatible with the specified collection
       * (<a href="../Collection.html#optional-restrictions">optional</a>)
       * @throws NullPointerException if this set contains a null element and the
       *         specified collection does not permit null elements
       * (<a href="../Collection.html#optional-restrictions">optional</a>),
       *         or if the specified collection is null
       * @see #remove(Object)
       */
      public boolean removeAll(Collection<?> c) {
          return al.removeAll(c);
      }
  
      /**
       * Retains only the elements in this set that are contained in the
       * specified collection.  In other words, removes from this set all of
       * its elements that are not contained in the specified collection.  If
       * the specified collection is also a set, this operation effectively
       * modifies this set so that its value is the <i>intersection</i> of the
       * two sets.
       *
       * @param  c collection containing elements to be retained in this set
       * @return {@code true} if this set changed as a result of the call
       * @throws ClassCastException if the class of an element of this set
       *         is incompatible with the specified collection
       * (<a href="../Collection.html#optional-restrictions">optional</a>)
       * @throws NullPointerException if this set contains a null element and the
       *         specified collection does not permit null elements
       * (<a href="../Collection.html#optional-restrictions">optional</a>),
       *         or if the specified collection is null
       * @see #remove(Object)
       */
      public boolean retainAll(Collection<?> c) {
          return al.retainAll(c);
      }
  
      /**
       * Returns an iterator over the elements contained in this set
       * in the order in which these elements were added.
       *
       * <p>The returned iterator provides a snapshot of the state of the set
       * when the iterator was constructed. No synchronization is needed while
       * traversing the iterator. The iterator does <em>NOT</em> support the
       * {@code remove} method.
       *
       * @return an iterator over the elements in this set
       */
      public Iterator<E> iterator() {
          return al.iterator();
      }
  
      /**
       * Compares the specified object with this set for equality.
       * Returns {@code true} if the specified object is the same object
       * as this object, or if it is also a {@link Set} and the elements
       * returned by an {@linkplain Set#iterator() iterator} over the
       * specified set are the same as the elements returned by an
       * iterator over this set.  More formally, the two iterators are
       * considered to return the same elements if they return the same
       * number of elements and for every element {@code e1} returned by
       * the iterator over the specified set, there is an element
       * {@code e2} returned by the iterator over this set such that
       * {@code Objects.equals(e1, e2)}.
       *
       * @param o object to be compared for equality with this set
       * @return {@code true} if the specified object is equal to this set
       */
      public boolean equals(Object o) {
          return (o == this)
              || ((o instanceof Set)
                  && compareSets(al.getArray(), (Set<?>) o) == 0);
      }
  
      public boolean removeIf(Predicate<? super E> filter) {
          return al.removeIf(filter);
      }
  
      public void forEach(Consumer<? super E> action) {
          al.forEach(action);
      }
  
      /**
       * Returns a {@link Spliterator} over the elements in this set in the order
       * in which these elements were added.
       *
       * <p>The {@code Spliterator} reports {@link Spliterator#IMMUTABLE},
       * {@link Spliterator#DISTINCT}, {@link Spliterator#SIZED}, and
       * {@link Spliterator#SUBSIZED}.
       *
       * <p>The spliterator provides a snapshot of the state of the set
       * when the spliterator was constructed. No synchronization is needed while
       * operating on the spliterator.
       *
       * @return a {@code Spliterator} over the elements in this set
       * @since 1.8
       */
      public Spliterator<E> spliterator() {
          return Spliterators.spliterator
              (al.getArray(), Spliterator.IMMUTABLE | Spliterator.DISTINCT);
      }
  }
  