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.util.function.LongBinaryOperator; import java.util.function.LongUnaryOperator; /** * A {@code long} array 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 */ public class AtomicLongArray implements java.io.Serializable { private static final long serialVersionUID = -2308431214976778248L; private static final VarHandle AA = MethodHandles.arrayElementVarHandle(long[].class); private final long[] array; /** * Creates a new AtomicLongArray of the given length, with all * elements initially zero. * * @param length the length of the array */ public AtomicLongArray(int length) { array = new long[length]; } /** * Creates a new AtomicLongArray 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 AtomicLongArray(long[] array) { // Visibility guaranteed by final field guarantees this.array = array.clone(); } /** * 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 */ public final long get(int i) { return (long) 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, long 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, long 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 */ public final long getAndSet(int i, long newValue) { return (long) 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, long expectedValue, long 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, long expectedValue, long 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, long expectedValue, long newValue) { return AA.weakCompareAndSetPlain(array, i, expectedValue, newValue); } /** * Atomically increments the value of the element at index {@code i}, * with memory effects as specified by {@link VarHandle#getAndAdd}. * * <p>Equivalent to {@code getAndAdd(i, 1)}. * * @param i the index * @return the previous value */ public final long getAndIncrement(int i) { return (long) AA.getAndAdd(array, i, 1L); } /** * Atomically decrements the value of the element at index {@code i}, * with memory effects as specified by {@link VarHandle#getAndAdd}. * * <p>Equivalent to {@code getAndAdd(i, -1)}. * * @param i the index * @return the previous value */ public final long getAndDecrement(int i) { return (long) AA.getAndAdd(array, i, -1L); } /** * Atomically adds the given value to the element at index {@code i}, * with memory effects as specified by {@link VarHandle#getAndAdd}. * * @param i the index * @param delta the value to add * @return the previous value */ public final long getAndAdd(int i, long delta) { return (long) AA.getAndAdd(array, i, delta); } /** * Atomically increments the value of the element at index {@code i}, * with memory effects as specified by {@link VarHandle#getAndAdd}. * * <p>Equivalent to {@code addAndGet(i, 1)}. * * @param i the index * @return the updated value */ public final long incrementAndGet(int i) { return (long) AA.getAndAdd(array, i, 1L) + 1L; } /** * Atomically decrements the value of the element at index {@code i}, * with memory effects as specified by {@link VarHandle#getAndAdd}. * * <p>Equivalent to {@code addAndGet(i, -1)}. * * @param i the index * @return the updated value */ public final long decrementAndGet(int i) { return (long) AA.getAndAdd(array, i, -1L) - 1L; } /** * Atomically adds the given value to the element at index {@code i}, * with memory effects as specified by {@link VarHandle#getAndAdd}. * * @param i the index * @param delta the value to add * @return the updated value */ public long addAndGet(int i, long delta) { return (long) AA.getAndAdd(array, i, delta) + delta; } /** * 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 long getAndUpdate(int i, LongUnaryOperator updateFunction) { long prev = get(i), next = 0L; for (boolean haveNext = false;;) { if (!haveNext) next = updateFunction.applyAsLong(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 long updateAndGet(int i, LongUnaryOperator updateFunction) { long prev = get(i), next = 0L; for (boolean haveNext = false;;) { if (!haveNext) next = updateFunction.applyAsLong(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 long getAndAccumulate(int i, long x, LongBinaryOperator accumulatorFunction) { long prev = get(i), next = 0L; for (boolean haveNext = false;;) { if (!haveNext) next = accumulatorFunction.applyAsLong(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 long accumulateAndGet(int i, long x, LongBinaryOperator accumulatorFunction) { long prev = get(i), next = 0L; for (boolean haveNext = false;;) { if (!haveNext) next = accumulatorFunction.applyAsLong(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(' '); } } // 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 long getPlain(int i) { return (long) 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, long 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 long getOpaque(int i) { return (long) 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, long 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 long getAcquire(int i) { return (long) 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, long 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 long compareAndExchange(int i, long expectedValue, long newValue) { return (long) 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 long compareAndExchangeAcquire(int i, long expectedValue, long newValue) { return (long) 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 long compareAndExchangeRelease(int i, long expectedValue, long newValue) { return (long) 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, long expectedValue, long 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, long expectedValue, long 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, long expectedValue, long newValue) { return AA.weakCompareAndSetRelease(array, i, expectedValue, newValue); } }