| 1 |
768 |
jeremybenn |
/*
|
| 2 |
|
|
* Written by Doug Lea with assistance from members of JCP JSR-166
|
| 3 |
|
|
* Expert Group and released to the public domain, as explained at
|
| 4 |
|
|
* http://creativecommons.org/licenses/publicdomain
|
| 5 |
|
|
*/
|
| 6 |
|
|
|
| 7 |
|
|
package java.util.concurrent.atomic;
|
| 8 |
|
|
|
| 9 |
|
|
/**
|
| 10 |
|
|
* An <tt>AtomicStampedReference</tt> maintains an object reference
|
| 11 |
|
|
* along with an integer "stamp", that can be updated atomically.
|
| 12 |
|
|
*
|
| 13 |
|
|
* <p> Implementation note. This implementation maintains stamped
|
| 14 |
|
|
* references by creating internal objects representing "boxed"
|
| 15 |
|
|
* [reference, integer] pairs.
|
| 16 |
|
|
*
|
| 17 |
|
|
* @since 1.5
|
| 18 |
|
|
* @author Doug Lea
|
| 19 |
|
|
* @param <V> The type of object referred to by this reference
|
| 20 |
|
|
*/
|
| 21 |
|
|
public class AtomicStampedReference<V> {
|
| 22 |
|
|
|
| 23 |
|
|
private static class ReferenceIntegerPair<T> {
|
| 24 |
|
|
private final T reference;
|
| 25 |
|
|
private final int integer;
|
| 26 |
|
|
ReferenceIntegerPair(T r, int i) {
|
| 27 |
|
|
reference = r; integer = i;
|
| 28 |
|
|
}
|
| 29 |
|
|
}
|
| 30 |
|
|
|
| 31 |
|
|
private final AtomicReference<ReferenceIntegerPair<V>> atomicRef;
|
| 32 |
|
|
|
| 33 |
|
|
/**
|
| 34 |
|
|
* Creates a new <tt>AtomicStampedReference</tt> with the given
|
| 35 |
|
|
* initial values.
|
| 36 |
|
|
*
|
| 37 |
|
|
* @param initialRef the initial reference
|
| 38 |
|
|
* @param initialStamp the initial stamp
|
| 39 |
|
|
*/
|
| 40 |
|
|
public AtomicStampedReference(V initialRef, int initialStamp) {
|
| 41 |
|
|
atomicRef = new AtomicReference<ReferenceIntegerPair<V>>
|
| 42 |
|
|
(new ReferenceIntegerPair<V>(initialRef, initialStamp));
|
| 43 |
|
|
}
|
| 44 |
|
|
|
| 45 |
|
|
/**
|
| 46 |
|
|
* Returns the current value of the reference.
|
| 47 |
|
|
*
|
| 48 |
|
|
* @return the current value of the reference
|
| 49 |
|
|
*/
|
| 50 |
|
|
public V getReference() {
|
| 51 |
|
|
return atomicRef.get().reference;
|
| 52 |
|
|
}
|
| 53 |
|
|
|
| 54 |
|
|
/**
|
| 55 |
|
|
* Returns the current value of the stamp.
|
| 56 |
|
|
*
|
| 57 |
|
|
* @return the current value of the stamp
|
| 58 |
|
|
*/
|
| 59 |
|
|
public int getStamp() {
|
| 60 |
|
|
return atomicRef.get().integer;
|
| 61 |
|
|
}
|
| 62 |
|
|
|
| 63 |
|
|
/**
|
| 64 |
|
|
* Returns the current values of both the reference and the stamp.
|
| 65 |
|
|
* Typical usage is <tt>int[1] holder; ref = v.get(holder); </tt>.
|
| 66 |
|
|
*
|
| 67 |
|
|
* @param stampHolder an array of size of at least one. On return,
|
| 68 |
|
|
* <tt>stampholder[0]</tt> will hold the value of the stamp.
|
| 69 |
|
|
* @return the current value of the reference
|
| 70 |
|
|
*/
|
| 71 |
|
|
public V get(int[] stampHolder) {
|
| 72 |
|
|
ReferenceIntegerPair<V> p = atomicRef.get();
|
| 73 |
|
|
stampHolder[0] = p.integer;
|
| 74 |
|
|
return p.reference;
|
| 75 |
|
|
}
|
| 76 |
|
|
|
| 77 |
|
|
/**
|
| 78 |
|
|
* Atomically sets the value of both the reference and stamp
|
| 79 |
|
|
* to the given update values if the
|
| 80 |
|
|
* current reference is <tt>==</tt> to the expected reference
|
| 81 |
|
|
* and the current stamp is equal to the expected stamp.
|
| 82 |
|
|
* May fail spuriously and does not provide ordering guarantees,
|
| 83 |
|
|
* so is only rarely an appropriate alternative to <tt>compareAndSet</tt>.
|
| 84 |
|
|
*
|
| 85 |
|
|
* @param expectedReference the expected value of the reference
|
| 86 |
|
|
* @param newReference the new value for the reference
|
| 87 |
|
|
* @param expectedStamp the expected value of the stamp
|
| 88 |
|
|
* @param newStamp the new value for the stamp
|
| 89 |
|
|
* @return true if successful
|
| 90 |
|
|
*/
|
| 91 |
|
|
public boolean weakCompareAndSet(V expectedReference,
|
| 92 |
|
|
V newReference,
|
| 93 |
|
|
int expectedStamp,
|
| 94 |
|
|
int newStamp) {
|
| 95 |
|
|
ReferenceIntegerPair<V> current = atomicRef.get();
|
| 96 |
|
|
return expectedReference == current.reference &&
|
| 97 |
|
|
expectedStamp == current.integer &&
|
| 98 |
|
|
((newReference == current.reference &&
|
| 99 |
|
|
newStamp == current.integer) ||
|
| 100 |
|
|
atomicRef.weakCompareAndSet(current,
|
| 101 |
|
|
new ReferenceIntegerPair<V>(newReference,
|
| 102 |
|
|
newStamp)));
|
| 103 |
|
|
}
|
| 104 |
|
|
|
| 105 |
|
|
/**
|
| 106 |
|
|
* Atomically sets the value of both the reference and stamp
|
| 107 |
|
|
* to the given update values if the
|
| 108 |
|
|
* current reference is <tt>==</tt> to the expected reference
|
| 109 |
|
|
* and the current stamp is equal to the expected stamp.
|
| 110 |
|
|
*
|
| 111 |
|
|
* @param expectedReference the expected value of the reference
|
| 112 |
|
|
* @param newReference the new value for the reference
|
| 113 |
|
|
* @param expectedStamp the expected value of the stamp
|
| 114 |
|
|
* @param newStamp the new value for the stamp
|
| 115 |
|
|
* @return true if successful
|
| 116 |
|
|
*/
|
| 117 |
|
|
public boolean compareAndSet(V expectedReference,
|
| 118 |
|
|
V newReference,
|
| 119 |
|
|
int expectedStamp,
|
| 120 |
|
|
int newStamp) {
|
| 121 |
|
|
ReferenceIntegerPair<V> current = atomicRef.get();
|
| 122 |
|
|
return expectedReference == current.reference &&
|
| 123 |
|
|
expectedStamp == current.integer &&
|
| 124 |
|
|
((newReference == current.reference &&
|
| 125 |
|
|
newStamp == current.integer) ||
|
| 126 |
|
|
atomicRef.compareAndSet(current,
|
| 127 |
|
|
new ReferenceIntegerPair<V>(newReference,
|
| 128 |
|
|
newStamp)));
|
| 129 |
|
|
}
|
| 130 |
|
|
|
| 131 |
|
|
|
| 132 |
|
|
/**
|
| 133 |
|
|
* Unconditionally sets the value of both the reference and stamp.
|
| 134 |
|
|
*
|
| 135 |
|
|
* @param newReference the new value for the reference
|
| 136 |
|
|
* @param newStamp the new value for the stamp
|
| 137 |
|
|
*/
|
| 138 |
|
|
public void set(V newReference, int newStamp) {
|
| 139 |
|
|
ReferenceIntegerPair<V> current = atomicRef.get();
|
| 140 |
|
|
if (newReference != current.reference || newStamp != current.integer)
|
| 141 |
|
|
atomicRef.set(new ReferenceIntegerPair<V>(newReference, newStamp));
|
| 142 |
|
|
}
|
| 143 |
|
|
|
| 144 |
|
|
/**
|
| 145 |
|
|
* Atomically sets the value of the stamp to the given update value
|
| 146 |
|
|
* if the current reference is <tt>==</tt> to the expected
|
| 147 |
|
|
* reference. Any given invocation of this operation may fail
|
| 148 |
|
|
* (return <tt>false</tt>) spuriously, but repeated invocation
|
| 149 |
|
|
* when the current value holds the expected value and no other
|
| 150 |
|
|
* thread is also attempting to set the value will eventually
|
| 151 |
|
|
* succeed.
|
| 152 |
|
|
*
|
| 153 |
|
|
* @param expectedReference the expected value of the reference
|
| 154 |
|
|
* @param newStamp the new value for the stamp
|
| 155 |
|
|
* @return true if successful
|
| 156 |
|
|
*/
|
| 157 |
|
|
public boolean attemptStamp(V expectedReference, int newStamp) {
|
| 158 |
|
|
ReferenceIntegerPair<V> current = atomicRef.get();
|
| 159 |
|
|
return expectedReference == current.reference &&
|
| 160 |
|
|
(newStamp == current.integer ||
|
| 161 |
|
|
atomicRef.compareAndSet(current,
|
| 162 |
|
|
new ReferenceIntegerPair<V>(expectedReference,
|
| 163 |
|
|
newStamp)));
|
| 164 |
|
|
}
|
| 165 |
|
|
}
|
