| /* |
| * 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; |
| |
| /** |
| * 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; |
| |
| private static final sun.misc.Unsafe U = sun.misc.Unsafe.getUnsafe(); |
| private static final long VALUE; |
| |
| static { |
| try { |
| VALUE = U.objectFieldOffset |
| (AtomicBoolean.class.getDeclaredField("value")); |
| } catch (ReflectiveOperationException e) { |
| throw new Error(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. |
| * |
| * @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) { |
| return U.compareAndSwapInt(this, VALUE, |
| (expect ? 1 : 0), |
| (update ? 1 : 0)); |
| } |
| |
| /** |
| * 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) { |
| return U.compareAndSwapInt(this, VALUE, |
| (expect ? 1 : 0), |
| (update ? 1 : 0)); |
| } |
| |
| /** |
| * 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) { |
| U.putOrderedInt(this, 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) { |
| 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()); |
| } |
| |
| } |