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--- old/src/share/classes/java/util/concurrent/atomic/AtomicStampedReference.java
+++ new/src/share/classes/java/util/concurrent/atomic/AtomicStampedReference.java
1 1 /*
2 2 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
3 3 *
4 4 * This code is free software; you can redistribute it and/or modify it
5 5 * under the terms of the GNU General Public License version 2 only, as
6 6 * published by the Free Software Foundation. Oracle designates this
7 7 * particular file as subject to the "Classpath" exception as provided
8 8 * by Oracle in the LICENSE file that accompanied this code.
9 9 *
10 10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 13 * version 2 for more details (a copy is included in the LICENSE file that
14 14 * accompanied this code).
15 15 *
16 16 * You should have received a copy of the GNU General Public License version
17 17 * 2 along with this work; if not, write to the Free Software Foundation,
18 18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 19 *
20 20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 21 * or visit www.oracle.com if you need additional information or have any
22 22 * questions.
23 23 */
24 24
25 25 /*
26 26 * This file is available under and governed by the GNU General Public
27 27 * License version 2 only, as published by the Free Software Foundation.
28 28 * However, the following notice accompanied the original version of this
29 29 * file:
30 30 *
31 31 * Written by Doug Lea with assistance from members of JCP JSR-166
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31 lines elided |
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32 32 * Expert Group and released to the public domain, as explained at
33 33 * http://creativecommons.org/licenses/publicdomain
34 34 */
35 35
36 36 package java.util.concurrent.atomic;
37 37
38 38 /**
39 39 * An {@code AtomicStampedReference} maintains an object reference
40 40 * along with an integer "stamp", that can be updated atomically.
41 41 *
42 - * <p> Implementation note. This implementation maintains stamped
42 + * <p>Implementation note: This implementation maintains stamped
43 43 * references by creating internal objects representing "boxed"
44 44 * [reference, integer] pairs.
45 45 *
46 46 * @since 1.5
47 47 * @author Doug Lea
48 48 * @param <V> The type of object referred to by this reference
49 49 */
50 -public class AtomicStampedReference<V> {
50 +public class AtomicStampedReference<V> {
51 51
52 - private static class ReferenceIntegerPair<T> {
53 - private final T reference;
54 - private final int integer;
55 - ReferenceIntegerPair(T r, int i) {
56 - reference = r; integer = i;
52 + private static class Pair<T> {
53 + final T reference;
54 + final int stamp;
55 + private Pair(T reference, int stamp) {
56 + this.reference = reference;
57 + this.stamp = stamp;
57 58 }
59 + static <T> Pair<T> of(T reference, int stamp) {
60 + return new Pair<T>(reference, stamp);
61 + }
58 62 }
59 63
60 - private final AtomicReference<ReferenceIntegerPair<V>> atomicRef;
64 + private volatile Pair<V> pair;
61 65
62 66 /**
63 67 * Creates a new {@code AtomicStampedReference} with the given
64 68 * initial values.
65 69 *
66 70 * @param initialRef the initial reference
67 71 * @param initialStamp the initial stamp
68 72 */
69 73 public AtomicStampedReference(V initialRef, int initialStamp) {
70 - atomicRef = new AtomicReference<ReferenceIntegerPair<V>>
71 - (new ReferenceIntegerPair<V>(initialRef, initialStamp));
74 + pair = Pair.of(initialRef, initialStamp);
72 75 }
73 76
74 77 /**
75 78 * Returns the current value of the reference.
76 79 *
77 80 * @return the current value of the reference
78 81 */
79 82 public V getReference() {
80 - return atomicRef.get().reference;
83 + return pair.reference;
81 84 }
82 85
83 86 /**
84 87 * Returns the current value of the stamp.
85 88 *
86 89 * @return the current value of the stamp
87 90 */
88 91 public int getStamp() {
89 - return atomicRef.get().integer;
92 + return pair.stamp;
90 93 }
91 94
92 95 /**
93 96 * Returns the current values of both the reference and the stamp.
94 97 * Typical usage is {@code int[1] holder; ref = v.get(holder); }.
95 98 *
96 99 * @param stampHolder an array of size of at least one. On return,
97 100 * {@code stampholder[0]} will hold the value of the stamp.
98 101 * @return the current value of the reference
99 102 */
100 103 public V get(int[] stampHolder) {
101 - ReferenceIntegerPair<V> p = atomicRef.get();
102 - stampHolder[0] = p.integer;
103 - return p.reference;
104 + Pair<V> pair = this.pair;
105 + stampHolder[0] = pair.stamp;
106 + return pair.reference;
104 107 }
105 108
106 109 /**
107 110 * Atomically sets the value of both the reference and stamp
108 111 * to the given update values if the
109 112 * current reference is {@code ==} to the expected reference
110 113 * and the current stamp is equal to the expected stamp.
111 114 *
112 115 * <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
113 116 * and does not provide ordering guarantees, so is only rarely an
114 117 * appropriate alternative to {@code compareAndSet}.
115 118 *
116 119 * @param expectedReference the expected value of the reference
117 120 * @param newReference the new value for the reference
118 121 * @param expectedStamp the expected value of the stamp
119 122 * @param newStamp the new value for the stamp
120 123 * @return true if successful
121 124 */
122 - public boolean weakCompareAndSet(V expectedReference,
123 - V newReference,
124 - int expectedStamp,
125 - int newStamp) {
126 - ReferenceIntegerPair<V> current = atomicRef.get();
127 - return expectedReference == current.reference &&
128 - expectedStamp == current.integer &&
129 - ((newReference == current.reference &&
130 - newStamp == current.integer) ||
131 - atomicRef.weakCompareAndSet(current,
132 - new ReferenceIntegerPair<V>(newReference,
133 - newStamp)));
125 + public boolean weakCompareAndSet(V expectedReference,
126 + V newReference,
127 + int expectedStamp,
128 + int newStamp) {
129 + return compareAndSet(expectedReference, newReference,
130 + expectedStamp, newStamp);
134 131 }
135 132
136 133 /**
137 134 * Atomically sets the value of both the reference and stamp
138 135 * to the given update values if the
139 136 * current reference is {@code ==} to the expected reference
140 137 * and the current stamp is equal to the expected stamp.
141 138 *
142 139 * @param expectedReference the expected value of the reference
143 140 * @param newReference the new value for the reference
144 141 * @param expectedStamp the expected value of the stamp
145 142 * @param newStamp the new value for the stamp
146 143 * @return true if successful
147 144 */
148 - public boolean compareAndSet(V expectedReference,
149 - V newReference,
150 - int expectedStamp,
151 - int newStamp) {
152 - ReferenceIntegerPair<V> current = atomicRef.get();
153 - return expectedReference == current.reference &&
154 - expectedStamp == current.integer &&
145 + public boolean compareAndSet(V expectedReference,
146 + V newReference,
147 + int expectedStamp,
148 + int newStamp) {
149 + Pair<V> current = pair;
150 + return
151 + expectedReference == current.reference &&
152 + expectedStamp == current.stamp &&
155 153 ((newReference == current.reference &&
156 - newStamp == current.integer) ||
157 - atomicRef.compareAndSet(current,
158 - new ReferenceIntegerPair<V>(newReference,
159 - newStamp)));
154 + newStamp == current.stamp) ||
155 + casPair(current, Pair.of(newReference, newStamp)));
160 156 }
161 157
162 158
163 159 /**
164 160 * Unconditionally sets the value of both the reference and stamp.
165 161 *
166 162 * @param newReference the new value for the reference
167 163 * @param newStamp the new value for the stamp
168 164 */
169 165 public void set(V newReference, int newStamp) {
170 - ReferenceIntegerPair<V> current = atomicRef.get();
171 - if (newReference != current.reference || newStamp != current.integer)
172 - atomicRef.set(new ReferenceIntegerPair<V>(newReference, newStamp));
166 + Pair<V> current = pair;
167 + if (newReference != current.reference || newStamp != current.stamp)
168 + this.pair = Pair.of(newReference, newStamp);
173 169 }
174 170
175 171 /**
176 172 * Atomically sets the value of the stamp to the given update value
177 173 * if the current reference is {@code ==} to the expected
178 174 * reference. Any given invocation of this operation may fail
179 175 * (return {@code false}) spuriously, but repeated invocation
180 176 * when the current value holds the expected value and no other
181 177 * thread is also attempting to set the value will eventually
182 178 * succeed.
183 179 *
184 180 * @param expectedReference the expected value of the reference
185 181 * @param newStamp the new value for the stamp
186 182 * @return true if successful
187 183 */
188 184 public boolean attemptStamp(V expectedReference, int newStamp) {
189 - ReferenceIntegerPair<V> current = atomicRef.get();
190 - return expectedReference == current.reference &&
191 - (newStamp == current.integer ||
192 - atomicRef.compareAndSet(current,
193 - new ReferenceIntegerPair<V>(expectedReference,
194 - newStamp)));
185 + Pair<V> current = pair;
186 + return
187 + expectedReference == current.reference &&
188 + (newStamp == current.stamp ||
189 + casPair(current, Pair.of(expectedReference, newStamp)));
195 190 }
191 +
192 + // Unsafe mechanics
193 +
194 + private static final sun.misc.Unsafe UNSAFE = sun.misc.Unsafe.getUnsafe();
195 + private static final long pairOffset =
196 + objectFieldOffset(UNSAFE, "pair", AtomicStampedReference.class);
197 +
198 + private boolean casPair(Pair<V> cmp, Pair<V> val) {
199 + return UNSAFE.compareAndSwapObject(this, pairOffset, cmp, val);
200 + }
201 +
202 + static long objectFieldOffset(sun.misc.Unsafe UNSAFE,
203 + String field, Class<?> klazz) {
204 + try {
205 + return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
206 + } catch (NoSuchFieldException e) {
207 + // Convert Exception to corresponding Error
208 + NoSuchFieldError error = new NoSuchFieldError(field);
209 + error.initCause(e);
210 + throw error;
211 + }
212 + }
196 213 }
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