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Diffstat (limited to 'libjava/classpath/external/jsr166/java/util/concurrent/atomic/AtomicStampedReference.java')
| -rw-r--r-- | libjava/classpath/external/jsr166/java/util/concurrent/atomic/AtomicStampedReference.java | 165 |
1 files changed, 165 insertions, 0 deletions
diff --git a/libjava/classpath/external/jsr166/java/util/concurrent/atomic/AtomicStampedReference.java b/libjava/classpath/external/jsr166/java/util/concurrent/atomic/AtomicStampedReference.java new file mode 100644 index 000000000..558808216 --- /dev/null +++ b/libjava/classpath/external/jsr166/java/util/concurrent/atomic/AtomicStampedReference.java @@ -0,0 +1,165 @@ +/* + * 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>AtomicStampedReference</tt> maintains an object reference + * along with an integer "stamp", that can be updated atomically. + * + * <p> Implementation note. This implementation maintains stamped + * references by creating internal objects representing "boxed" + * [reference, integer] pairs. + * + * @since 1.5 + * @author Doug Lea + * @param <V> The type of object referred to by this reference + */ +public class AtomicStampedReference<V> { + + private static class ReferenceIntegerPair<T> { + private final T reference; + private final int integer; + ReferenceIntegerPair(T r, int i) { + reference = r; integer = i; + } + } + + private final AtomicReference<ReferenceIntegerPair<V>> atomicRef; + + /** + * Creates a new <tt>AtomicStampedReference</tt> with the given + * initial values. + * + * @param initialRef the initial reference + * @param initialStamp the initial stamp + */ + public AtomicStampedReference(V initialRef, int initialStamp) { + atomicRef = new AtomicReference<ReferenceIntegerPair<V>> + (new ReferenceIntegerPair<V>(initialRef, initialStamp)); + } + + /** + * 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 stamp. + * + * @return the current value of the stamp + */ + public int getStamp() { + return atomicRef.get().integer; + } + + /** + * Returns the current values of both the reference and the stamp. + * Typical usage is <tt>int[1] holder; ref = v.get(holder); </tt>. + * + * @param stampHolder an array of size of at least one. On return, + * <tt>stampholder[0]</tt> will hold the value of the stamp. + * @return the current value of the reference + */ + public V get(int[] stampHolder) { + ReferenceIntegerPair<V> p = atomicRef.get(); + stampHolder[0] = p.integer; + return p.reference; + } + + /** + * Atomically sets the value of both the reference and stamp + * to the given update values if the + * current reference is <tt>==</tt> to the expected reference + * and the current stamp is equal to the expected stamp. + * 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 expectedStamp the expected value of the stamp + * @param newStamp the new value for the stamp + * @return true if successful + */ + public boolean weakCompareAndSet(V expectedReference, + V newReference, + int expectedStamp, + int newStamp) { + ReferenceIntegerPair<V> current = atomicRef.get(); + return expectedReference == current.reference && + expectedStamp == current.integer && + ((newReference == current.reference && + newStamp == current.integer) || + atomicRef.weakCompareAndSet(current, + new ReferenceIntegerPair<V>(newReference, + newStamp))); + } + + /** + * Atomically sets the value of both the reference and stamp + * to the given update values if the + * current reference is <tt>==</tt> to the expected reference + * and the current stamp is equal to the expected stamp. + * + * @param expectedReference the expected value of the reference + * @param newReference the new value for the reference + * @param expectedStamp the expected value of the stamp + * @param newStamp the new value for the stamp + * @return true if successful + */ + public boolean compareAndSet(V expectedReference, + V newReference, + int expectedStamp, + int newStamp) { + ReferenceIntegerPair<V> current = atomicRef.get(); + return expectedReference == current.reference && + expectedStamp == current.integer && + ((newReference == current.reference && + newStamp == current.integer) || + atomicRef.compareAndSet(current, + new ReferenceIntegerPair<V>(newReference, + newStamp))); + } + + + /** + * Unconditionally sets the value of both the reference and stamp. + * + * @param newReference the new value for the reference + * @param newStamp the new value for the stamp + */ + public void set(V newReference, int newStamp) { + ReferenceIntegerPair<V> current = atomicRef.get(); + if (newReference != current.reference || newStamp != current.integer) + atomicRef.set(new ReferenceIntegerPair<V>(newReference, newStamp)); + } + + /** + * Atomically sets the value of the stamp 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 newStamp the new value for the stamp + * @return true if successful + */ + public boolean attemptStamp(V expectedReference, int newStamp) { + ReferenceIntegerPair<V> current = atomicRef.get(); + return expectedReference == current.reference && + (newStamp == current.integer || + atomicRef.compareAndSet(current, + new ReferenceIntegerPair<V>(expectedReference, + newStamp))); + } +} |