Java tutorial
/* * 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); 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); 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); } }