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Diffstat (limited to 'libjava/classpath/external/jsr166/java/util/concurrent/atomic/AtomicBoolean.java')
-rw-r--r-- | libjava/classpath/external/jsr166/java/util/concurrent/atomic/AtomicBoolean.java | 133 |
1 files changed, 133 insertions, 0 deletions
diff --git a/libjava/classpath/external/jsr166/java/util/concurrent/atomic/AtomicBoolean.java b/libjava/classpath/external/jsr166/java/util/concurrent/atomic/AtomicBoolean.java new file mode 100644 index 00000000000..bd823bd2c23 --- /dev/null +++ b/libjava/classpath/external/jsr166/java/util/concurrent/atomic/AtomicBoolean.java @@ -0,0 +1,133 @@ +/* + * 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 + */ + +package java.util.concurrent.atomic; +import sun.misc.Unsafe; + +/** + * 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; + // 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 <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 unsafe.compareAndSwapInt(this, valueOffset, e, u); + } + + /** + * 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) { + 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()); + } + +} |