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/*
 * 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 sun.misc.Unsafe;

/**
 * A {@code boolean} value that may be updated atomically. See the
 * {@link java.util.concurrent.atomic} package specification for
 * description of the properties of atomic variables. 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;
    // setup to use Unsafe.compareAndSwapInt for updates
    private static final Unsafe unsafe = Unsafe.getUnsafe();
    private static final long valueOffset;

    static {
        try {
            valueOffset = unsafe.objectFieldOffset
                (AtomicBoolean.class.getDeclaredField("value"));
        } catch (Exception ex) { throw new Error(ex); }
    }

    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.
     *
     * @return the current value
     */
    public final boolean get() {
        return value != 0;
    }

    /**
     * Atomically sets the value to the given updated value
     * if the current value {@code ==} the expected value.
     *
     * @param expect the expected value
     * @param update the new value
     * @return true if successful. False return indicates that
     * the actual value was not equal to the expected value.
     */
    public final boolean compareAndSet(boolean expect, boolean update) {
        int e = expect ? 1 : 0;
        int u = update ? 1 : 0;
        return unsafe.compareAndSwapInt(this, valueOffset, e, u);
    }

    /**
     * Atomically sets the value to the given updated value
     * if the current value {@code ==} the expected value.
     *
     * 

May fail * spuriously and does not provide ordering guarantees, so is * only rarely an appropriate alternative to {@code compareAndSet}. * * @param expect the expected value * @param update the new value * @return true if successful */ public boolean weakCompareAndSet(boolean expect, boolean update) { int e = expect ? 1 : 0; int u = update ? 1 : 0; return unsafe.compareAndSwapInt(this, valueOffset, e, u); } /** * Unconditionally sets to the given value. * * @param newValue the new value */ public final void set(boolean newValue) { value = newValue ? 1 : 0; } /** * Eventually sets to the given value. * * @param newValue the new value * @since 1.6 */ public final void lazySet(boolean newValue) { int v = newValue ? 1 : 0; unsafe.putOrderedInt(this, valueOffset, v); } /** * Atomically sets to the given value and returns the previous value. * * @param newValue the new value * @return the previous value */ public final boolean getAndSet(boolean newValue) { for (;;) { boolean current = get(); if (compareAndSet(current, newValue)) return current; } } /** * Returns the String representation of the current value. * @return the String representation of the current value */ public String toString() { return Boolean.toString(get()); } }





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