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; /** * A {@code boolean} value that may be updated atomically. See the * {@link VarHandle} specification for descriptions of the properties * of atomic accesses. An {@code AtomicBoolean} is used in * applications such as atomically updated flags, and cannot be used * as a replacement for a {@link java.lang.Boolean}. * * @since 1.5 * @author Doug Lea */ public class AtomicBoolean implements java.io.Serializable { private static final long serialVersionUID = 4654671469794556979L; private static final VarHandle VALUE; static { try { MethodHandles.Lookup l = MethodHandles.lookup(); VALUE = l.findVarHandle(AtomicBoolean.class, "value", int.class); } catch (ReflectiveOperationException e) { throw new ExceptionInInitializerError(e); } } private volatile int value; /** * Creates a new {@code AtomicBoolean} with the given initial value. * * @param initialValue the initial value */ public AtomicBoolean(boolean initialValue) { value = initialValue ? 1 : 0; } /** * Creates a new {@code AtomicBoolean} with initial value {@code false}. */ public AtomicBoolean() { } /** * Returns the current value, * with memory effects as specified by {@link VarHandle#getVolatile}. * * @return the current value */ public final boolean get() { return value != 0; } /** * Atomically sets the value to {@code newValue} * if the current value {@code == expectedValue}, * with memory effects as specified by {@link VarHandle#compareAndSet}. * * @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(boolean expectedValue, boolean newValue) { return VALUE.compareAndSet(this, (expectedValue ? 1 : 0), (newValue ? 1 : 0)); } /** * Possibly atomically sets the value to {@code newValue} * if the 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 expectedValue the expected value * @param newValue the new value * @return {@code true} if successful * @see #weakCompareAndSetPlain */ @Deprecated(since = "9") public boolean weakCompareAndSet(boolean expectedValue, boolean newValue) { return VALUE.weakCompareAndSetPlain(this, (expectedValue ? 1 : 0), (newValue ? 1 : 0)); } /** * Possibly atomically sets the value to {@code newValue} * if the current value {@code == expectedValue}, * with memory effects as specified by {@link VarHandle#weakCompareAndSetPlain}. * * @param expectedValue the expected value * @param newValue the new value * @return {@code true} if successful * @since 9 */ public boolean weakCompareAndSetPlain(boolean expectedValue, boolean newValue) { return VALUE.weakCompareAndSetPlain(this, (expectedValue ? 1 : 0), (newValue ? 1 : 0)); } /** * Sets the value to {@code newValue}, * with memory effects as specified by {@link VarHandle#setVolatile}. * * @param newValue the new value */ public final void set(boolean newValue) { value = newValue ? 1 : 0; } /** * Sets the value to {@code newValue}, * with memory effects as specified by {@link VarHandle#setRelease}. * * @param newValue the new value * @since 1.6 */ public final void lazySet(boolean newValue) { VALUE.setRelease(this, (newValue ? 1 : 0)); } /** * Atomically sets the value to {@code newValue} and returns the old value, * with memory effects as specified by {@link VarHandle#getAndSet}. * * @param newValue the new value * @return the previous value */ public final boolean getAndSet(boolean newValue) { return (int) VALUE.getAndSet(this, (newValue ? 1 : 0)) != 0; } /** * Returns the String representation of the current value. * @return the String representation of the current value */ public String toString() { return Boolean.toString(get()); } // jdk9 /** * Returns the current value, with memory semantics of reading as * if the variable was declared non-{@code volatile}. * * @return the value * @since 9 */ public final boolean getPlain() { return (int) VALUE.get(this) != 0; } /** * Sets the value to {@code newValue}, with memory semantics * of setting as if the variable was declared non-{@code volatile} * and non-{@code final}. * * @param newValue the new value * @since 9 */ public final void setPlain(boolean newValue) { VALUE.set(this, newValue ? 1 : 0); } /** * Returns the current value, * with memory effects as specified by {@link VarHandle#getOpaque}. * * @return the value * @since 9 */ public final boolean getOpaque() { return (int) VALUE.getOpaque(this) != 0; } /** * Sets the value to {@code newValue}, * with memory effects as specified by {@link VarHandle#setOpaque}. * * @param newValue the new value * @since 9 */ public final void setOpaque(boolean newValue) { VALUE.setOpaque(this, newValue ? 1 : 0); } /** * Returns the current value, * with memory effects as specified by {@link VarHandle#getAcquire}. * * @return the value * @since 9 */ public final boolean getAcquire() { return (int) VALUE.getAcquire(this) != 0; } /** * Sets the value to {@code newValue}, * with memory effects as specified by {@link VarHandle#setRelease}. * * @param newValue the new value * @since 9 */ public final void setRelease(boolean newValue) { VALUE.setRelease(this, newValue ? 1 : 0); } /** * Atomically sets the value to {@code newValue} if the current value, * referred to as the <em>witness value</em>, {@code == expectedValue}, * with memory effects as specified by * {@link VarHandle#compareAndExchange}. * * @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 boolean compareAndExchange(boolean expectedValue, boolean newValue) { return (int) VALUE.compareAndExchange(this, (expectedValue ? 1 : 0), (newValue ? 1 : 0)) != 0; } /** * Atomically sets the value to {@code newValue} if the current value, * referred to as the <em>witness value</em>, {@code == expectedValue}, * with memory effects as specified by * {@link VarHandle#compareAndExchangeAcquire}. * * @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 boolean compareAndExchangeAcquire(boolean expectedValue, boolean newValue) { return (int) VALUE.compareAndExchangeAcquire(this, (expectedValue ? 1 : 0), (newValue ? 1 : 0)) != 0; } /** * Atomically sets the value to {@code newValue} if the current value, * referred to as the <em>witness value</em>, {@code == expectedValue}, * with memory effects as specified by * {@link VarHandle#compareAndExchangeRelease}. * * @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 boolean compareAndExchangeRelease(boolean expectedValue, boolean newValue) { return (int) VALUE.compareAndExchangeRelease(this, (expectedValue ? 1 : 0), (newValue ? 1 : 0)) != 0; } /** * Possibly atomically sets the value to {@code newValue} if the current * value {@code == expectedValue}, * with memory effects as specified by * {@link VarHandle#weakCompareAndSet}. * * @param expectedValue the expected value * @param newValue the new value * @return {@code true} if successful * @since 9 */ public final boolean weakCompareAndSetVolatile(boolean expectedValue, boolean newValue) { return VALUE.weakCompareAndSet(this, (expectedValue ? 1 : 0), (newValue ? 1 : 0)); } /** * Possibly atomically sets the value to {@code newValue} if the current * value {@code == expectedValue}, * with memory effects as specified by * {@link VarHandle#weakCompareAndSetAcquire}. * * @param expectedValue the expected value * @param newValue the new value * @return {@code true} if successful * @since 9 */ public final boolean weakCompareAndSetAcquire(boolean expectedValue, boolean newValue) { return VALUE.weakCompareAndSetAcquire(this, (expectedValue ? 1 : 0), (newValue ? 1 : 0)); } /** * Possibly atomically sets the value to {@code newValue} if the current * value {@code == expectedValue}, * with memory effects as specified by * {@link VarHandle#weakCompareAndSetRelease}. * * @param expectedValue the expected value * @param newValue the new value * @return {@code true} if successful * @since 9 */ public final boolean weakCompareAndSetRelease(boolean expectedValue, boolean newValue) { return VALUE.weakCompareAndSetRelease(this, (expectedValue ? 1 : 0), (newValue ? 1 : 0)); } }