208 lines
7.4 KiB
Java
208 lines
7.4 KiB
Java
/*
|
|
* 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. Oracle designates this
|
|
* particular file as subject to the "Classpath" exception as provided
|
|
* by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
|
|
* or visit www.oracle.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/publicdomain/zero/1.0/
|
|
*/
|
|
|
|
package java.util.concurrent.atomic;
|
|
|
|
import java.lang.invoke.MethodHandles;
|
|
import java.lang.invoke.VarHandle;
|
|
|
|
/**
|
|
* 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 Pair<T> {
|
|
final T reference;
|
|
final int stamp;
|
|
private Pair(T reference, int stamp) {
|
|
this.reference = reference;
|
|
this.stamp = stamp;
|
|
}
|
|
static <T> Pair<T> of(T reference, int stamp) {
|
|
return new Pair<T>(reference, stamp);
|
|
}
|
|
}
|
|
|
|
private volatile Pair<V> pair;
|
|
|
|
/**
|
|
* 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) {
|
|
pair = Pair.of(initialRef, initialStamp);
|
|
}
|
|
|
|
/**
|
|
* Returns the current value of the reference.
|
|
*
|
|
* @return the current value of the reference
|
|
*/
|
|
public V getReference() {
|
|
return pair.reference;
|
|
}
|
|
|
|
/**
|
|
* Returns the current value of the stamp.
|
|
*
|
|
* @return the current value of the stamp
|
|
*/
|
|
public int getStamp() {
|
|
return pair.stamp;
|
|
}
|
|
|
|
/**
|
|
* 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) {
|
|
Pair<V> pair = this.pair;
|
|
stampHolder[0] = pair.stamp;
|
|
return pair.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. This operation may fail spuriously 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 {@code true} if successful
|
|
*/
|
|
public boolean weakCompareAndSet(V expectedReference,
|
|
V newReference,
|
|
int expectedStamp,
|
|
int newStamp) {
|
|
return compareAndSet(expectedReference, newReference,
|
|
expectedStamp, 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 {@code true} if successful
|
|
*/
|
|
public boolean compareAndSet(V expectedReference,
|
|
V newReference,
|
|
int expectedStamp,
|
|
int newStamp) {
|
|
Pair<V> current = pair;
|
|
return
|
|
expectedReference == current.reference &&
|
|
expectedStamp == current.stamp &&
|
|
((newReference == current.reference &&
|
|
newStamp == current.stamp) ||
|
|
casPair(current, Pair.of(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) {
|
|
Pair<V> current = pair;
|
|
if (newReference != current.reference || newStamp != current.stamp)
|
|
this.pair = Pair.of(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 {@code true} if successful
|
|
*/
|
|
public boolean attemptStamp(V expectedReference, int newStamp) {
|
|
Pair<V> current = pair;
|
|
return
|
|
expectedReference == current.reference &&
|
|
(newStamp == current.stamp ||
|
|
casPair(current, Pair.of(expectedReference, newStamp)));
|
|
}
|
|
|
|
// VarHandle mechanics
|
|
private static final VarHandle PAIR;
|
|
static {
|
|
try {
|
|
MethodHandles.Lookup l = MethodHandles.lookup();
|
|
PAIR = l.findVarHandle(AtomicStampedReference.class, "pair",
|
|
Pair.class);
|
|
} catch (ReflectiveOperationException e) {
|
|
throw new ExceptionInInitializerError(e);
|
|
}
|
|
}
|
|
|
|
private boolean casPair(Pair<V> cmp, Pair<V> val) {
|
|
return PAIR.compareAndSet(this, cmp, val);
|
|
}
|
|
}
|