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.atomic;
  
  import java.lang.reflect.Array;
  import java.util.Arrays;
  import java.util.function.BinaryOperator;
  import java.util.function.UnaryOperator;
  
  /**
   * An array of object references in which elements may be updated
   * atomically.  See the {@link java.util.concurrent.atomic} package
   * specification for description of the properties of atomic
   * variables.
   * @since 1.5
   * @author Doug Lea
   * @param <E> The base class of elements held in this array
   */
  public class AtomicReferenceArray<E> implements java.io.Serializable {
      private static final long serialVersionUID = -6209656149925076980L;
  
      private static final sun.misc.Unsafe U = sun.misc.Unsafe.getUnsafe();
      private static final long ARRAY;
      private static final int ABASE;
      private static final int ASHIFT;
      private final Object[] array; // must have exact type Object[]
  
      static {
          try {
              ARRAY = U.objectFieldOffset
                  (AtomicReferenceArray.class.getDeclaredField("array"));
              ABASE = U.arrayBaseOffset(Object[].class);
              int scale = U.arrayIndexScale(Object[].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);
          }
      }
  
      private long checkedByteOffset(int i) {
          if (i < 0 || i >= array.length)
              throw new IndexOutOfBoundsException("index " + i);
  
          return byteOffset(i);
      }
  
      private static long byteOffset(int i) {
          return ((long) i << ASHIFT) + ABASE;
      }
  
      /**
       * Creates a new AtomicReferenceArray of the given length, with all
       * elements initially null.
       *
       * @param length the length of the array
       */
      public AtomicReferenceArray(int length) {
          array = new Object[length];
      }
  
      /**
       * Creates a new AtomicReferenceArray with the same length as, and
       * all elements copied from, the given array.
       *
       * @param array the array to copy elements from
       * @throws NullPointerException if array is null
       */
      public AtomicReferenceArray(E[] array) {
          // Visibility guaranteed by final field guarantees
          this.array = Arrays.copyOf(array, array.length, Object[].class);
      }
  
      /**
       * Returns the length of the array.
       *
       * @return the length of the array
       */
      public final int length() {
          return array.length;
      }
  
      /**
       * Gets the current value at position {@code i}.
       *
       * @param i the index
       * @return the current value
       */
      public final E get(int i) {
          return getRaw(checkedByteOffset(i));
      }
  
      @SuppressWarnings("unchecked")
      private E getRaw(long offset) {
          return (E) U.getObjectVolatile(array, offset);
      }
  
      /**
       * Sets the element at position {@code i} to the given value.
       *
       * @param i the index
       * @param newValue the new value
       */
      public final void set(int i, E newValue) {
          U.putObjectVolatile(array, checkedByteOffset(i), newValue);
      }
  
      /**
       * Eventually sets the element at position {@code i} to the given value.
       *
       * @param i the index
       * @param newValue the new value
       * @since 1.6
       */
      public final void lazySet(int i, E newValue) {
          U.putOrderedObject(array, checkedByteOffset(i), newValue);
      }
  
      /**
       * Atomically sets the element at position {@code i} to the given
       * value and returns the old value.
       *
       * @param i the index
       * @param newValue the new value
       * @return the previous value
       */
      @SuppressWarnings("unchecked")
      public final E getAndSet(int i, E newValue) {
          return (E)U.getAndSetObject(array, checkedByteOffset(i), newValue);
      }
  
      /**
       * Atomically sets the element at position {@code i} to the given
       * updated value if the current value {@code ==} the expected value.
       *
       * @param i the index
       * @param expect the expected value
       * @param update the new value
       * @return {@code true} if successful. False return indicates that
       * the actual value was not equal to the expected value.
       */
      public final boolean compareAndSet(int i, E expect, E update) {
          return compareAndSetRaw(checkedByteOffset(i), expect, update);
      }
  
      private boolean compareAndSetRaw(long offset, E expect, E update) {
          return U.compareAndSwapObject(array, offset, expect, update);
      }
  
      /**
       * Atomically sets the element at position {@code i} to the given
       * updated value if the current value {@code ==} the expected value.
       *
       * <p><a href="package-summary.html#weakCompareAndSet">May fail
       * spuriously and does not provide ordering guarantees</a>, so is
       * only rarely an appropriate alternative to {@code compareAndSet}.
       *
       * @param i the index
       * @param expect the expected value
       * @param update the new value
       * @return {@code true} if successful
       */
      public final boolean weakCompareAndSet(int i, E expect, E update) {
          return compareAndSet(i, expect, update);
      }
  
      /**
       * Atomically updates the element at index {@code i} with the results
       * of applying the given function, returning the previous value. The
       * function should be side-effect-free, since it may be re-applied
       * when attempted updates fail due to contention among threads.
       *
       * @param i the index
       * @param updateFunction a side-effect-free function
       * @return the previous value
       * @since 1.8
       */
      public final E getAndUpdate(int i, UnaryOperator<E> updateFunction) {
          long offset = checkedByteOffset(i);
          E prev, next;
          do {
              prev = getRaw(offset);
              next = updateFunction.apply(prev);
          } while (!compareAndSetRaw(offset, prev, next));
          return prev;
      }
  
      /**
       * Atomically updates the element at index {@code i} with the results
       * of applying the given function, returning the updated value. The
       * function should be side-effect-free, since it may be re-applied
       * when attempted updates fail due to contention among threads.
       *
       * @param i the index
       * @param updateFunction a side-effect-free function
       * @return the updated value
       * @since 1.8
       */
      public final E updateAndGet(int i, UnaryOperator<E> updateFunction) {
          long offset = checkedByteOffset(i);
          E prev, next;
          do {
              prev = getRaw(offset);
              next = updateFunction.apply(prev);
          } while (!compareAndSetRaw(offset, prev, next));
          return next;
      }
  
      /**
       * Atomically updates the element at index {@code i} with the
       * results of applying the given function to the current and
       * given values, returning the previous value. The function should
       * be side-effect-free, since it may be re-applied when attempted
       * updates fail due to contention among threads.  The function is
       * applied with the current value at index {@code i} as its first
       * argument, and the given update as the second argument.
       *
       * @param i the index
       * @param x the update value
       * @param accumulatorFunction a side-effect-free function of two arguments
       * @return the previous value
       * @since 1.8
       */
      public final E getAndAccumulate(int i, E x,
                                      BinaryOperator<E> accumulatorFunction) {
          long offset = checkedByteOffset(i);
          E prev, next;
          do {
              prev = getRaw(offset);
              next = accumulatorFunction.apply(prev, x);
          } while (!compareAndSetRaw(offset, prev, next));
          return prev;
      }
  
      /**
       * Atomically updates the element at index {@code i} with the
       * results of applying the given function to the current and
       * given values, returning the updated value. The function should
       * be side-effect-free, since it may be re-applied when attempted
       * updates fail due to contention among threads.  The function is
       * applied with the current value at index {@code i} as its first
       * argument, and the given update as the second argument.
       *
       * @param i the index
       * @param x the update value
       * @param accumulatorFunction a side-effect-free function of two arguments
       * @return the updated value
       * @since 1.8
       */
      public final E accumulateAndGet(int i, E x,
                                      BinaryOperator<E> accumulatorFunction) {
          long offset = checkedByteOffset(i);
          E prev, next;
          do {
              prev = getRaw(offset);
              next = accumulatorFunction.apply(prev, x);
          } while (!compareAndSetRaw(offset, prev, next));
          return next;
      }
  
      /**
       * Returns the String representation of the current values of array.
       * @return the String representation of the current values of array
       */
      public String toString() {
          int iMax = array.length - 1;
          if (iMax == -1)
              return "[]";
  
          StringBuilder b = new StringBuilder();
          b.append('[');
          for (int i = 0; ; i++) {
              b.append(getRaw(byteOffset(i)));
              if (i == iMax)
                  return b.append(']').toString();
              b.append(',').append(' ');
          }
      }
  
      /**
       * 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 {
          // Note: This must be changed if any additional fields are defined
          Object a = s.readFields().get("array", null);
          if (a == null || !a.getClass().isArray())
              throw new java.io.InvalidObjectException("Not array type");
          if (a.getClass() != Object[].class)
              a = Arrays.copyOf((Object[])a, Array.getLength(a), Object[].class);
          U.putObjectVolatile(this, ARRAY, a);
      }
  
  }
  