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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.
 *
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/*
 * 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 boolean value that may be updated atomically. See the VarHandle specification for descriptions of the properties of atomic accesses. An AtomicBoolean is used in applications such as atomically updated flags, and cannot be used as a replacement for a Boolean. 
Author:Doug Lea
Since:1.5
/**
 * 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 AtomicBoolean with the given initial value. 
Params:
  • initialValue – the initial 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 AtomicBoolean with initial value false. 
/**
     * Creates a new {@code AtomicBoolean} with initial value {@code false}.
     */
    public AtomicBoolean() {
    }

    
Returns the current value, with memory effects as specified by VarHandle.getVolatile. 
Returns:the current value
/**
     * 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 newValue if the current value == expectedValue, with memory effects as specified by VarHandle.compareAndSet. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
Returns:true if successful. False return indicates that the actual value was not equal to the expected value.
/**
     * 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 newValue if the current value == expectedValue, with memory effects as specified by VarHandle.weakCompareAndSetPlain. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
See Also:
Deprecated:This method has plain memory effects but the method name implies volatile memory effects (see methods such as compareAndExchange and compareAndSet). To avoid confusion over plain or volatile memory effects it is recommended that the method weakCompareAndSetPlain be used instead.
Returns:true if successful
/**
     * 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 newValue if the current value == expectedValue, with memory effects as specified by VarHandle.weakCompareAndSetPlain. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
Returns:true if successful
Since:9
/**
     * 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 newValue, with memory effects as specified by VarHandle.setVolatile. 
Params:
  • newValue – the new value
/**
     * 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 newValue, with memory effects as specified by VarHandle.setRelease. 
Params:
  • newValue – the new value
Since:1.6
/**
     * 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 newValue and returns the old value, with memory effects as specified by VarHandle.getAndSet. 
Params:
  • newValue – the new value
Returns:the previous value
/**
     * 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.

Returns:the String representation of the current value
/**
     * 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-volatile. 
Returns:the value
Since:9
/**
     * 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 newValue, with memory semantics of setting as if the variable was declared non-volatile and non-final. 
Params:
  • newValue – the new value
Since:9
/**
     * 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 VarHandle.getOpaque. 
Returns:the value
Since:9
/**
     * 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 newValue, with memory effects as specified by VarHandle.setOpaque. 
Params:
  • newValue – the new value
Since:9
/**
     * 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 VarHandle.getAcquire. 
Returns:the value
Since:9
/**
     * 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 newValue, with memory effects as specified by VarHandle.setRelease. 
Params:
  • newValue – the new value
Since:9
/**
     * 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 newValue if the current value, referred to as the witness value, == expectedValue, with memory effects as specified by VarHandle.compareAndExchange. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
Returns:the witness value, which will be the same as the
expected value if successful
Since:9
/**
     * 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 newValue if the current value, referred to as the witness value, == expectedValue, with memory effects as specified by VarHandle.compareAndExchangeAcquire. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
Returns:the witness value, which will be the same as the
expected value if successful
Since:9
/**
     * 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 newValue if the current value, referred to as the witness value, == expectedValue, with memory effects as specified by VarHandle.compareAndExchangeRelease. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
Returns:the witness value, which will be the same as the
expected value if successful
Since:9
/**
     * 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 newValue if the current value == expectedValue, with memory effects as specified by VarHandle.weakCompareAndSet. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
Returns:true if successful
Since:9
/**
     * 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 newValue if the current value == expectedValue, with memory effects as specified by VarHandle.weakCompareAndSetAcquire. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
Returns:true if successful
Since:9
/**
     * 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 newValue if the current value == expectedValue, with memory effects as specified by VarHandle.weakCompareAndSetRelease. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
Returns:true if successful
Since:9
/**
     * 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));
    }

}