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	/*
	* 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.util.function.UnaryOperator;
	import java.util.function.BinaryOperator;
	import java.util.Arrays;
	import java.lang.reflect.Array;
	import sun.misc.Unsafe;

	/**
	* 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 Unsafe unsafe;
	private static final int base;
	private static final int shift;
	private static final long arrayFieldOffset;
	private final Object[] array; // must have exact type Object[]

	static {
	try {
	unsafe = Unsafe.getUnsafe();
	arrayFieldOffset = unsafe.objectFieldOffset
	(AtomicReferenceArray.class.getDeclaredField("array"));
	base = unsafe.arrayBaseOffset(Object[].class);
	int scale = unsafe.arrayIndexScale(Object[].class);
	if ((scale & (scale - 1)) != 0)
	throw new Error("data type scale not a power of two");
	shift = 31 - Integer.numberOfLeadingZeros(scale);
	} catch (Exception 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 << shift) + base;
	}

	/**
	* 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) unsafe.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) {
	unsafe.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) {
	unsafe.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)unsafe.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 unsafe.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).
	*/
	private void readObject(java.io.ObjectInputStream s)
	throws java.io.IOException, ClassNotFoundException,
	java.io.InvalidObjectException {
	// 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);
	unsafe.putObjectVolatile(this, arrayFieldOffset, a);
	}

	}

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