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--- old/src/share/classes/java/util/concurrent/atomic/AtomicReferenceArray.java
+++ new/src/share/classes/java/util/concurrent/atomic/AtomicReferenceArray.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
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 import sun.misc.Unsafe;
38 38 import java.util.*;
39 39
40 40 /**
41 41 * An array of object references in which elements may be updated
42 42 * atomically. See the {@link java.util.concurrent.atomic} package
43 43 * specification for description of the properties of atomic
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43 lines elided |
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44 44 * variables.
45 45 * @since 1.5
46 46 * @author Doug Lea
47 47 * @param <E> The base class of elements held in this array
48 48 */
49 49 public class AtomicReferenceArray<E> implements java.io.Serializable {
50 50 private static final long serialVersionUID = -6209656149925076980L;
51 51
52 52 private static final Unsafe unsafe = Unsafe.getUnsafe();
53 53 private static final int base = unsafe.arrayBaseOffset(Object[].class);
54 - private static final int scale = unsafe.arrayIndexScale(Object[].class);
54 + private static final int shift;
55 55 private final Object[] array;
56 56
57 - private long rawIndex(int i) {
57 + static {
58 + int scale = unsafe.arrayIndexScale(Object[].class);
59 + if ((scale & (scale - 1)) != 0)
60 + throw new Error("data type scale not a power of two");
61 + shift = 31 - Integer.numberOfLeadingZeros(scale);
62 + }
63 +
64 + private long checkedByteOffset(int i) {
58 65 if (i < 0 || i >= array.length)
59 66 throw new IndexOutOfBoundsException("index " + i);
60 - return base + (long) i * scale;
67 +
68 + return byteOffset(i);
61 69 }
62 70
71 + private static long byteOffset(int i) {
72 + return ((long) i << shift) + base;
73 + }
74 +
63 75 /**
64 - * Creates a new AtomicReferenceArray of given length.
76 + * Creates a new AtomicReferenceArray of the given length, with all
77 + * elements initially zero.
78 + *
65 79 * @param length the length of the array
66 80 */
67 81 public AtomicReferenceArray(int length) {
68 82 array = new Object[length];
69 - // must perform at least one volatile write to conform to JMM
70 - if (length > 0)
71 - unsafe.putObjectVolatile(array, rawIndex(0), null);
72 83 }
73 84
74 85 /**
75 86 * Creates a new AtomicReferenceArray with the same length as, and
76 87 * all elements copied from, the given array.
77 88 *
78 89 * @param array the array to copy elements from
79 90 * @throws NullPointerException if array is null
80 91 */
81 92 public AtomicReferenceArray(E[] array) {
82 - if (array == null)
83 - throw new NullPointerException();
84 - int length = array.length;
85 - this.array = new Object[length];
86 - if (length > 0) {
87 - int last = length-1;
88 - for (int i = 0; i < last; ++i)
89 - this.array[i] = array[i];
90 - // Do the last write as volatile
91 - E e = array[last];
92 - unsafe.putObjectVolatile(this.array, rawIndex(last), e);
93 - }
93 + // Visibility guaranteed by final field guarantees
94 + this.array = array.clone();
94 95 }
95 96
96 97 /**
97 98 * Returns the length of the array.
98 99 *
99 100 * @return the length of the array
100 101 */
101 102 public final int length() {
102 103 return array.length;
103 104 }
104 105
105 106 /**
106 107 * Gets the current value at position {@code i}.
107 108 *
108 109 * @param i the index
109 110 * @return the current value
110 111 */
111 112 public final E get(int i) {
112 - return (E) unsafe.getObjectVolatile(array, rawIndex(i));
113 + return getRaw(checkedByteOffset(i));
113 114 }
114 115
116 + private E getRaw(long offset) {
117 + return (E) unsafe.getObjectVolatile(array, offset);
118 + }
119 +
115 120 /**
116 121 * Sets the element at position {@code i} to the given value.
117 122 *
118 123 * @param i the index
119 124 * @param newValue the new value
120 125 */
121 126 public final void set(int i, E newValue) {
122 - unsafe.putObjectVolatile(array, rawIndex(i), newValue);
127 + unsafe.putObjectVolatile(array, checkedByteOffset(i), newValue);
123 128 }
124 129
125 130 /**
126 131 * Eventually sets the element at position {@code i} to the given value.
127 132 *
128 133 * @param i the index
129 134 * @param newValue the new value
130 135 * @since 1.6
131 136 */
132 137 public final void lazySet(int i, E newValue) {
133 - unsafe.putOrderedObject(array, rawIndex(i), newValue);
138 + unsafe.putOrderedObject(array, checkedByteOffset(i), newValue);
134 139 }
135 140
136 141
137 142 /**
138 143 * Atomically sets the element at position {@code i} to the given
139 144 * value and returns the old value.
140 145 *
141 146 * @param i the index
142 147 * @param newValue the new value
143 148 * @return the previous value
144 149 */
145 150 public final E getAndSet(int i, E newValue) {
151 + long offset = checkedByteOffset(i);
146 152 while (true) {
147 - E current = get(i);
148 - if (compareAndSet(i, current, newValue))
153 + E current = (E) getRaw(offset);
154 + if (compareAndSetRaw(offset, current, newValue))
149 155 return current;
150 156 }
151 157 }
152 158
153 159 /**
154 160 * Atomically sets the element at position {@code i} to the given
155 161 * updated value if the current value {@code ==} the expected value.
162 + *
156 163 * @param i the index
157 164 * @param expect the expected value
158 165 * @param update the new value
159 166 * @return true if successful. False return indicates that
160 167 * the actual value was not equal to the expected value.
161 168 */
162 169 public final boolean compareAndSet(int i, E expect, E update) {
163 - return unsafe.compareAndSwapObject(array, rawIndex(i),
164 - expect, update);
170 + return compareAndSetRaw(checkedByteOffset(i), expect, update);
165 171 }
166 172
173 + private boolean compareAndSetRaw(long offset, E expect, E update) {
174 + return unsafe.compareAndSwapObject(array, offset, expect, update);
175 + }
176 +
167 177 /**
168 178 * Atomically sets the element at position {@code i} to the given
169 179 * updated value if the current value {@code ==} the expected value.
170 180 *
171 181 * <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
172 182 * and does not provide ordering guarantees, so is only rarely an
173 183 * appropriate alternative to {@code compareAndSet}.
174 184 *
175 185 * @param i the index
176 186 * @param expect the expected value
177 187 * @param update the new value
178 188 * @return true if successful.
179 189 */
180 190 public final boolean weakCompareAndSet(int i, E expect, E update) {
181 191 return compareAndSet(i, expect, update);
182 192 }
183 193
184 194 /**
185 195 * Returns the String representation of the current values of array.
186 - * @return the String representation of the current values of array.
196 + * @return the String representation of the current values of array
187 197 */
188 198 public String toString() {
189 - if (array.length > 0) // force volatile read
190 - get(0);
191 - return Arrays.toString(array);
199 + int iMax = array.length - 1;
200 + if (iMax == -1)
201 + return "[]";
202 +
203 + StringBuilder b = new StringBuilder();
204 + b.append('[');
205 + for (int i = 0; ; i++) {
206 + b.append(getRaw(byteOffset(i)));
207 + if (i == iMax)
208 + return b.append(']').toString();
209 + b.append(',').append(' ');
210 + }
192 211 }
193 212
194 213 }
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