AtomicBoolean.java

/*
 * 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/licenses/publicdomain
 *
 * Modified for IKVM.NET by Jeroen Frijters
 */

/*
  Parts Copyright (C) 2006 Jeroen Frijters

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.

  Jeroen Frijters
  jeroen@frijters.net
  
*/

package java.util.concurrent.atomic;

/**
 * A <tt>boolean</tt> value that may be updated atomically. See the
 * {@link java.util.concurrent.atomic} package specification for
 * description of the properties of atomic variables. An
 * <tt>AtomicBoolean</tt> 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 volatile int value;

    /**
     * Creates a new <tt>AtomicBoolean</tt> with the given initial value.
     *
     * @param initialValue the initial value
     */
    public AtomicBoolean(boolean initialValue) {
        value = initialValue ? 1 : 0;
    }

    /**
     * Creates a new <tt>AtomicBoolean</tt> with initial value <tt>false</tt>.
     */
    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 <tt>==</tt> 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 compareAndSwapInt(e, u);
    }
    // implemented in map.xml
    private native boolean compareAndSwapInt(int expected, int update);

    /**
     * Atomically sets the value to the given updated value
     * if the current value <tt>==</tt> the expected value.
     * May fail spuriously and does not provide ordering guarantees,
     * so is only rarely an appropriate alternative to <tt>compareAndSet</tt>.
     *
     * @param expect the expected value
     * @param update the new value
     * @return true if successful.
     */
    public boolean weakCompareAndSet(boolean expect, boolean update) {
        return compareAndSet(expect, update);
    }

    /**
     * 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) {
        value = newValue ? 1 : 0;
    }

    /**
     * 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());
    }

}