Back to index...

	/*
	* 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.invoke.MethodHandles;
	import java.lang.invoke.VarHandle;
	import java.lang.reflect.Array;
	import java.lang.reflect.Field;
	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 VarHandle} specification for
	* descriptions of the properties of atomic accesses.
	* @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 VarHandle AA
	= MethodHandles.arrayElementVarHandle(Object[].class);
	@SuppressWarnings("serial") // Conditionally serializable
	private final Object[] array; // must have exact type Object[]

	/**
	* 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;
	}

	/**
	* Returns the current value of the element at index {@code i},
	* with memory effects as specified by {@link VarHandle#getVolatile}.
	*
	* @param i the index
	* @return the current value
	*/
	@SuppressWarnings("unchecked")
	public final E get(int i) {
	return (E)AA.getVolatile(array, i);
	}

	/**
	* Sets the element at index {@code i} to {@code newValue},
	* with memory effects as specified by {@link VarHandle#setVolatile}.
	*
	* @param i the index
	* @param newValue the new value
	*/
	public final void set(int i, E newValue) {
	AA.setVolatile(array, i, newValue);
	}

	/**
	* Sets the element at index {@code i} to {@code newValue},
	* with memory effects as specified by {@link VarHandle#setRelease}.
	*
	* @param i the index
	* @param newValue the new value
	* @since 1.6
	*/
	public final void lazySet(int i, E newValue) {
	AA.setRelease(array, i, newValue);
	}

	/**
	* Atomically sets the element at index {@code i} to {@code
	* newValue} and returns the old value,
	* with memory effects as specified by {@link VarHandle#getAndSet}.
	*
	* @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)AA.getAndSet(array, i, newValue);
	}

	/**
	* Atomically sets the element at index {@code i} to {@code newValue}
	* if the element's current value {@code == expectedValue},
	* with memory effects as specified by {@link VarHandle#compareAndSet}.
	*
	* @param i the index
	* @param expectedValue the expected value
	* @param newValue 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 expectedValue, E newValue) {
	return AA.compareAndSet(array, i, expectedValue, newValue);
	}

	/**
	* Possibly atomically sets the element at index {@code i} to
	* {@code newValue} if the element's current value {@code == expectedValue},
	* with memory effects as specified by {@link VarHandle#weakCompareAndSetPlain}.
	*
	* @deprecated This method has plain memory effects but the method
	* name implies volatile memory effects (see methods such as
	* {@link #compareAndExchange} and {@link #compareAndSet}). To avoid
	* confusion over plain or volatile memory effects it is recommended that
	* the method {@link #weakCompareAndSetPlain} be used instead.
	*
	* @param i the index
	* @param expectedValue the expected value
	* @param newValue the new value
	* @return {@code true} if successful
	* @see #weakCompareAndSetPlain
	*/
	@Deprecated(since="9")
	public final boolean weakCompareAndSet(int i, E expectedValue, E newValue) {
	return AA.weakCompareAndSetPlain(array, i, expectedValue, newValue);
	}

	/**
	* Possibly atomically sets the element at index {@code i} to
	* {@code newValue} if the element's current value {@code == expectedValue},
	* with memory effects as specified by {@link VarHandle#weakCompareAndSetPlain}.
	*
	* @param i the index
	* @param expectedValue the expected value
	* @param newValue the new value
	* @return {@code true} if successful
	* @since 9
	*/
	public final boolean weakCompareAndSetPlain(int i, E expectedValue, E newValue) {
	return AA.weakCompareAndSetPlain(array, i, expectedValue, newValue);
	}

	/**
	* Atomically updates (with memory effects as specified by {@link
	* VarHandle#compareAndSet}) 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) {
	E prev = get(i), next = null;
	for (boolean haveNext = false;;) {
	if (!haveNext)
	next = updateFunction.apply(prev);
	if (weakCompareAndSetVolatile(i, prev, next))
	return prev;
	haveNext = (prev == (prev = get(i)));
	}
	}

	/**
	* Atomically updates (with memory effects as specified by {@link
	* VarHandle#compareAndSet}) 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) {
	E prev = get(i), next = null;
	for (boolean haveNext = false;;) {
	if (!haveNext)
	next = updateFunction.apply(prev);
	if (weakCompareAndSetVolatile(i, prev, next))
	return next;
	haveNext = (prev == (prev = get(i)));
	}
	}

	/**
	* Atomically updates (with memory effects as specified by {@link
	* VarHandle#compareAndSet}) 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 of the element 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) {
	E prev = get(i), next = null;
	for (boolean haveNext = false;;) {
	if (!haveNext)
	next = accumulatorFunction.apply(prev, x);
	if (weakCompareAndSetVolatile(i, prev, next))
	return prev;
	haveNext = (prev == (prev = get(i)));
	}
	}

	/**
	* Atomically updates (with memory effects as specified by {@link
	* VarHandle#compareAndSet}) 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 of the element 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) {
	E prev = get(i), next = null;
	for (boolean haveNext = false;;) {
	if (!haveNext)
	next = accumulatorFunction.apply(prev, x);
	if (weakCompareAndSetVolatile(i, prev, next))
	return next;
	haveNext = (prev == (prev = get(i)));
	}
	}

	/**
	* 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(get(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);
	@SuppressWarnings("removal")
	Field arrayField = java.security.AccessController.doPrivileged(
	(java.security.PrivilegedAction<Field>) () -> {
	try {
	Field f = AtomicReferenceArray.class
	.getDeclaredField("array");
	f.setAccessible(true);
	return f;
	} catch (ReflectiveOperationException e) {
	throw new Error(e);
	}});
	try {
	arrayField.set(this, a);
	} catch (IllegalAccessException e) {
	throw new Error(e);
	}
	}

	// jdk9

	/**
	* Returns the current value of the element at index {@code i},
	* with memory semantics of reading as if the variable was declared
	* non-{@code volatile}.
	*
	* @param i the index
	* @return the value
	* @since 9
	*/
	public final E getPlain(int i) {
	return (E)AA.get(array, i);
	}

	/**
	* Sets the element at index {@code i} to {@code newValue},
	* with memory semantics of setting as if the variable was
	* declared non-{@code volatile} and non-{@code final}.
	*
	* @param i the index
	* @param newValue the new value
	* @since 9
	*/
	public final void setPlain(int i, E newValue) {
	AA.set(array, i, newValue);
	}

	/**
	* Returns the current value of the element at index {@code i},
	* with memory effects as specified by {@link VarHandle#getOpaque}.
	*
	* @param i the index
	* @return the value
	* @since 9
	*/
	public final E getOpaque(int i) {
	return (E)AA.getOpaque(array, i);
	}

	/**
	* Sets the element at index {@code i} to {@code newValue},
	* with memory effects as specified by {@link VarHandle#setOpaque}.
	*
	* @param i the index
	* @param newValue the new value
	* @since 9
	*/
	public final void setOpaque(int i, E newValue) {
	AA.setOpaque(array, i, newValue);
	}

	/**
	* Returns the current value of the element at index {@code i},
	* with memory effects as specified by {@link VarHandle#getAcquire}.
	*
	* @param i the index
	* @return the value
	* @since 9
	*/
	public final E getAcquire(int i) {
	return (E)AA.getAcquire(array, i);
	}

	/**
	* Sets the element at index {@code i} to {@code newValue},
	* with memory effects as specified by {@link VarHandle#setRelease}.
	*
	* @param i the index
	* @param newValue the new value
	* @since 9
	*/
	public final void setRelease(int i, E newValue) {
	AA.setRelease(array, i, newValue);
	}

	/**
	* Atomically sets the element at index {@code i} to {@code newValue}
	* if the element's current value, referred to as the <em>witness
	* value</em>, {@code == expectedValue},
	* with memory effects as specified by
	* {@link VarHandle#compareAndExchange}.
	*
	* @param i the index
	* @param expectedValue the expected value
	* @param newValue the new value
	* @return the witness value, which will be the same as the
	* expected value if successful
	* @since 9
	*/
	public final E compareAndExchange(int i, E expectedValue, E newValue) {
	return (E)AA.compareAndExchange(array, i, expectedValue, newValue);
	}

	/**
	* Atomically sets the element at index {@code i} to {@code newValue}
	* if the element's current value, referred to as the <em>witness
	* value</em>, {@code == expectedValue},
	* with memory effects as specified by
	* {@link VarHandle#compareAndExchangeAcquire}.
	*
	* @param i the index
	* @param expectedValue the expected value
	* @param newValue the new value
	* @return the witness value, which will be the same as the
	* expected value if successful
	* @since 9
	*/
	public final E compareAndExchangeAcquire(int i, E expectedValue, E newValue) {
	return (E)AA.compareAndExchangeAcquire(array, i, expectedValue, newValue);
	}

	/**
	* Atomically sets the element at index {@code i} to {@code newValue}
	* if the element's current value, referred to as the <em>witness
	* value</em>, {@code == expectedValue},
	* with memory effects as specified by
	* {@link VarHandle#compareAndExchangeRelease}.
	*
	* @param i the index
	* @param expectedValue the expected value
	* @param newValue the new value
	* @return the witness value, which will be the same as the
	* expected value if successful
	* @since 9
	*/
	public final E compareAndExchangeRelease(int i, E expectedValue, E newValue) {
	return (E)AA.compareAndExchangeRelease(array, i, expectedValue, newValue);
	}

	/**
	* Possibly atomically sets the element at index {@code i} to
	* {@code newValue} if the element's current value {@code == expectedValue},
	* with memory effects as specified by
	* {@link VarHandle#weakCompareAndSet}.
	*
	* @param i the index
	* @param expectedValue the expected value
	* @param newValue the new value
	* @return {@code true} if successful
	* @since 9
	*/
	public final boolean weakCompareAndSetVolatile(int i, E expectedValue, E newValue) {
	return AA.weakCompareAndSet(array, i, expectedValue, newValue);
	}

	/**
	* Possibly atomically sets the element at index {@code i} to
	* {@code newValue} if the element's current value {@code == expectedValue},
	* with memory effects as specified by
	* {@link VarHandle#weakCompareAndSetAcquire}.
	*
	* @param i the index
	* @param expectedValue the expected value
	* @param newValue the new value
	* @return {@code true} if successful
	* @since 9
	*/
	public final boolean weakCompareAndSetAcquire(int i, E expectedValue, E newValue) {
	return AA.weakCompareAndSetAcquire(array, i, expectedValue, newValue);
	}

	/**
	* Possibly atomically sets the element at index {@code i} to
	* {@code newValue} if the element's current value {@code == expectedValue},
	* with memory effects as specified by
	* {@link VarHandle#weakCompareAndSetRelease}.
	*
	* @param i the index
	* @param expectedValue the expected value
	* @param newValue the new value
	* @return {@code true} if successful
	* @since 9
	*/
	public final boolean weakCompareAndSetRelease(int i, E expectedValue, E newValue) {
	return AA.weakCompareAndSetRelease(array, i, expectedValue, newValue);
	}

	}

Back to index...