| /* |
| * 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 {@code AtomicMarkableReference} 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 {@code AtomicMarkableReference} 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 {@code boolean[1] holder; ref = v.get(holder); }. |
| * |
| * @param markHolder an array of size of at least one. On return, |
| * {@code markholder[0]} 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 {@code ==} to the expected reference |
| * and the current mark is equal to the expected mark. |
| * |
| * <p>May <a href="package-summary.html#Spurious">fail spuriously</a> |
| * and does not provide ordering guarantees, so is only rarely an |
| * appropriate alternative to {@code compareAndSet}. |
| * |
| * @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 {@code ==} 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 {@code ==} to the expected |
| * reference. Any given invocation of this operation may fail |
| * (return {@code false}) 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))); |
| } |
| } |