--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/src/share/classes/java/util/concurrent/atomic/AtomicStampedReference.java Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,196 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Sun designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Sun in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * 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 AtomicStampedReference} 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 {@code AtomicStampedReference} 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 {@code int[1] holder; ref = v.get(holder); }.
+ *
+ * @param stampHolder an array of size of at least one. On return,
+ * {@code stampholder[0]} 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 {@code ==} to the expected reference
+ * and the current stamp is equal to the expected stamp.
+ *
+ * <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 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 {@code ==} 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 {@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 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)));
+ }
+}