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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* This file is available under and governed by the GNU General Public
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* License version 2 only, as published by the Free Software Foundation.
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* However, the following notice accompanied the original version of this
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/publicdomain/zero/1.0/
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package java.util.concurrent.atomic;
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import java.lang.reflect.Array;
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import java.util.Arrays;
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import sun.misc.Unsafe;
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* An array of object references in which elements may be updated
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* atomically. See the {@link java.util.concurrent.atomic} package
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* specification for description of the properties of atomic
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* @param <E> The base class of elements held in this array
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public class AtomicReferenceArray<E> implements java.io.Serializable {
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private static final long serialVersionUID = -6209656149925076980L;
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private static final Unsafe unsafe;
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private static final long arrayFieldOffset;
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private final Object[] array; // must have exact type Object[]
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unsafe = Unsafe.getUnsafe();
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arrayFieldOffset = unsafe.objectFieldOffset
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(AtomicReferenceArray.class.getDeclaredField("array"));
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} catch (Exception e) {
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* Creates a new AtomicReferenceArray of the given length, with all
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* elements initially null.
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* @param length the length of the array
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public AtomicReferenceArray(int length) {
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array = new Object[length];
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* Creates a new AtomicReferenceArray with the same length as, and
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* all elements copied from, the given array.
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* @param array the array to copy elements from
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* @throws NullPointerException if array is null
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public AtomicReferenceArray(E[] array) {
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// Visibility guaranteed by final field guarantees
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this.array = Arrays.copyOf(array, array.length, Object[].class);
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* Returns the length of the array.
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* @return the length of the array
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public final int length() {
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* Gets the current value at position {@code i}.
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* @return the current value
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public final native E get(int i);
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* Sets the element at position {@code i} to the given value.
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* @param newValue the new value
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public final native void set(int i, E newValue);
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* Eventually sets the element at position {@code i} to the given value.
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* @param newValue the new value
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public final void lazySet(int i, E newValue) {
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* Atomically sets the element at position {@code i} to the given
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* value and returns the old value.
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* @param newValue the new value
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* @return the previous value
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public final E getAndSet(int i, E newValue) {
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if (compareAndSet(i, current, newValue))
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* Atomically sets the element at position {@code i} to the given
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* updated value if the current value {@code ==} the expected value.
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* @param expect the expected value
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* @param update the new value
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* @return true if successful. False return indicates that
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* the actual value was not equal to the expected value.
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public final native boolean compareAndSet(int i, E expect, E update);
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* Atomically sets the element at position {@code i} to the given
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* updated value if the current value {@code ==} the expected value.
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* <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
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* and does not provide ordering guarantees, so is only rarely an
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* appropriate alternative to {@code compareAndSet}.
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* @param expect the expected value
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* @param update the new value
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* @return true if successful.
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public final boolean weakCompareAndSet(int i, E expect, E update) {
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return compareAndSet(i, expect, update);
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* Returns the String representation of the current values of array.
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* @return the String representation of the current values of array
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public String toString() {
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int iMax = array.length - 1;
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StringBuilder b = new StringBuilder();
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for (int i = 0; ; i++) {
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return b.append(']').toString();
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b.append(',').append(' ');
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* Reconstitutes the instance from a stream (that is, deserializes it).
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* @param s the stream
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private void readObject(java.io.ObjectInputStream s)
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throws java.io.IOException, ClassNotFoundException {
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// Note: This must be changed if any additional fields are defined
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Object a = s.readFields().get("array", null);
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if (a == null || !a.getClass().isArray())
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throw new java.io.InvalidObjectException("Not array type");
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if (a.getClass() != Object[].class)
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a = Arrays.copyOf((Object[])a, Array.getLength(a), Object[].class);
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unsafe.putObjectVolatile(this, arrayFieldOffset, a);