/*

 * 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 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 {@code 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.

     *

     * <p><a href="package-summary.html#weakCompareAndSet">May fail

     * spuriously and does not provide ordering guarantees</a>, so is

     * only rarely an appropriate alternative to {@code compareAndSet}.

     *

     * @param expect the expected value

     * @param update the new value

     * @return {@code 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) {

        boolean prev;

        do {

            prev = get();

        } while (!compareAndSet(prev, newValue));

        return prev;

    }

    /**

     * Returns the String representation of the current value.

     * @return the String representation of the current value

     */

    public String toString() {

        return Boolean.toString(get());

    }

}