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Diffstat (limited to 'libjava/classpath/external/jsr166/java/util/concurrent/atomic/AtomicMarkableReference.java')
| -rw-r--r-- | libjava/classpath/external/jsr166/java/util/concurrent/atomic/AtomicMarkableReference.java | 161 |
1 files changed, 161 insertions, 0 deletions
diff --git a/libjava/classpath/external/jsr166/java/util/concurrent/atomic/AtomicMarkableReference.java b/libjava/classpath/external/jsr166/java/util/concurrent/atomic/AtomicMarkableReference.java new file mode 100644 index 000000000..85335b737 --- /dev/null +++ b/libjava/classpath/external/jsr166/java/util/concurrent/atomic/AtomicMarkableReference.java @@ -0,0 +1,161 @@ +/* + * 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; + +/** + * An <tt>AtomicMarkableReference</tt> maintains an object reference + * along with a mark bit, that can be updated atomically. + * <p> + * <p> Implementation note. This implementation maintains markable + * references by creating internal objects representing "boxed" + * [reference, boolean] pairs. + * + * @since 1.5 + * @author Doug Lea + * @param <V> The type of object referred to by this reference + */ +public class AtomicMarkableReference<V> { + + private static class ReferenceBooleanPair<T> { + private final T reference; + private final boolean bit; + ReferenceBooleanPair(T r, boolean i) { + reference = r; bit = i; + } + } + + private final AtomicReference<ReferenceBooleanPair<V>> atomicRef; + + /** + * Creates a new <tt>AtomicMarkableReference</tt> with the given + * initial values. + * + * @param initialRef the initial reference + * @param initialMark the initial mark + */ + public AtomicMarkableReference(V initialRef, boolean initialMark) { + atomicRef = new AtomicReference<ReferenceBooleanPair<V>> (new ReferenceBooleanPair<V>(initialRef, initialMark)); + } + + /** + * Returns the current value of the reference. + * + * @return the current value of the reference + */ + public V getReference() { + return atomicRef.get().reference; + } + + /** + * Returns the current value of the mark. + * + * @return the current value of the mark + */ + public boolean isMarked() { + return atomicRef.get().bit; + } + + /** + * Returns the current values of both the reference and the mark. + * Typical usage is <tt>boolean[1] holder; ref = v.get(holder); </tt>. + * + * @param markHolder an array of size of at least one. On return, + * <tt>markholder[0]</tt> will hold the value of the mark. + * @return the current value of the reference + */ + public V get(boolean[] markHolder) { + ReferenceBooleanPair<V> p = atomicRef.get(); + markHolder[0] = p.bit; + return p.reference; + } + + /** + * Atomically sets the value of both the reference and mark + * to the given update values if the + * current reference is <tt>==</tt> to the expected reference + * and the current mark is equal to the expected mark. + * May fail spuriously and does not provide ordering guarantees, + * so is only rarely an appropriate alternative to <tt>compareAndSet</tt>. + * + * @param expectedReference the expected value of the reference + * @param newReference the new value for the reference + * @param expectedMark the expected value of the mark + * @param newMark the new value for the mark + * @return true if successful + */ + public boolean weakCompareAndSet(V expectedReference, + V newReference, + boolean expectedMark, + boolean newMark) { + ReferenceBooleanPair<V> current = atomicRef.get(); + return expectedReference == current.reference && + expectedMark == current.bit && + ((newReference == current.reference && newMark == current.bit) || + atomicRef.weakCompareAndSet(current, + new ReferenceBooleanPair<V>(newReference, + newMark))); + } + + /** + * Atomically sets the value of both the reference and mark + * to the given update values if the + * current reference is <tt>==</tt> to the expected reference + * and the current mark is equal to the expected mark. + * + * @param expectedReference the expected value of the reference + * @param newReference the new value for the reference + * @param expectedMark the expected value of the mark + * @param newMark the new value for the mark + * @return true if successful + */ + public boolean compareAndSet(V expectedReference, + V newReference, + boolean expectedMark, + boolean newMark) { + ReferenceBooleanPair<V> current = atomicRef.get(); + return expectedReference == current.reference && + expectedMark == current.bit && + ((newReference == current.reference && newMark == current.bit) || + atomicRef.compareAndSet(current, + new ReferenceBooleanPair<V>(newReference, + newMark))); + } + + /** + * Unconditionally sets the value of both the reference and mark. + * + * @param newReference the new value for the reference + * @param newMark the new value for the mark + */ + public void set(V newReference, boolean newMark) { + ReferenceBooleanPair<V> current = atomicRef.get(); + if (newReference != current.reference || newMark != current.bit) + atomicRef.set(new ReferenceBooleanPair<V>(newReference, newMark)); + } + + /** + * Atomically sets the value of the mark to the given update value + * if the current reference is <tt>==</tt> to the expected + * reference. Any given invocation of this operation may fail + * (return <tt>false</tt>) spuriously, but repeated invocation + * when the current value holds the expected value and no other + * thread is also attempting to set the value will eventually + * succeed. + * + * @param expectedReference the expected value of the reference + * @param newMark the new value for the mark + * @return true if successful + */ + public boolean attemptMark(V expectedReference, boolean newMark) { + ReferenceBooleanPair<V> current = atomicRef.get(); + return expectedReference == current.reference && + (newMark == current.bit || + atomicRef.compareAndSet + (current, new ReferenceBooleanPair<V>(expectedReference, + newMark))); + } +} |