1 /*
2 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation. Oracle designates this
7 * particular file as subject to the "Classpath" exception as provided
8 * by Oracle in the LICENSE file that accompanied this code.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 */
24
25 /*
26 * This file is available under and governed by the GNU General Public
27 * License version 2 only, as published by the Free Software Foundation.
28 * However, the following notice accompanied the original version of this
29 * file:
30 *
31 * Written by Doug Lea with assistance from members of JCP JSR-166
32 * Expert Group and released to the public domain, as explained at
33 * http://creativecommons.org/publicdomain/zero/1.0/
34 */
35
36 package java.util.concurrent.atomic;
37 import sun.misc.Unsafe;
38
39 /**
40 * A {@code long} array in which elements may be updated atomically.
41 * See the {@link java.util.concurrent.atomic} package specification
42 * for description of the properties of atomic variables.
43 * @since 1.5
44 * @author Doug Lea
45 */
46 public class AtomicLongArray implements java.io.Serializable {
47 private static final long serialVersionUID = -2308431214976778248L;
48
49 private static final Unsafe unsafe = Unsafe.getUnsafe();
50 private static final int base = unsafe.arrayBaseOffset(long[].class);
51 private static final int shift;
52 private final long[] array;
53
54 static {
55 int scale = unsafe.arrayIndexScale(long[].class);
56 if ((scale & (scale - 1)) != 0)
57 throw new Error("data type scale not a power of two");
58 shift = 31 - Integer.numberOfLeadingZeros(scale);
59 }
60
61 private long checkedByteOffset(int i) {
62 if (i < 0 || i >= array.length)
63 throw new IndexOutOfBoundsException("index " + i);
64
65 return byteOffset(i);
66 }
67
68 private static long byteOffset(int i) {
69 return ((long) i << shift) + base;
70 }
71
72 /**
73 * Creates a new AtomicLongArray of the given length, with all
74 * elements initially zero.
75 *
76 * @param length the length of the array
77 */
78 public AtomicLongArray(int length) {
79 array = new long[length];
80 }
81
82 /**
83 * Creates a new AtomicLongArray with the same length as, and
84 * all elements copied from, the given array.
85 *
86 * @param array the array to copy elements from
87 * @throws NullPointerException if array is null
88 */
89 public AtomicLongArray(long[] array) {
90 // Visibility guaranteed by final field guarantees
91 this.array = array.clone();
92 }
93
94 /**
95 * Returns the length of the array.
96 *
97 * @return the length of the array
98 */
99 public final int length() {
100 return array.length;
101 }
102
103 /**
104 * Gets the current value at position {@code i}.
105 *
106 * @param i the index
107 * @return the current value
108 */
109 public final long get(int i) {
110 return getRaw(checkedByteOffset(i));
111 }
112
113 private long getRaw(long offset) {
114 return unsafe.getLongVolatile(array, offset);
115 }
116
117 /**
118 * Sets the element at position {@code i} to the given value.
119 *
120 * @param i the index
121 * @param newValue the new value
122 */
123 public final void set(int i, long newValue) {
124 unsafe.putLongVolatile(array, checkedByteOffset(i), newValue);
125 }
126
127 /**
128 * Eventually sets the element at position {@code i} to the given value.
129 *
130 * @param i the index
131 * @param newValue the new value
132 * @since 1.6
133 */
134 public final void lazySet(int i, long newValue) {
135 unsafe.putOrderedLong(array, checkedByteOffset(i), newValue);
136 }
137
138 /**
139 * Atomically sets the element at position {@code i} to the given value
140 * and returns the old value.
141 *
142 * @param i the index
143 * @param newValue the new value
144 * @return the previous value
145 */
146 public final long getAndSet(int i, long newValue) {
147 return unsafe.getAndSetLong(array, checkedByteOffset(i), newValue);
148 }
149
150 /**
151 * Atomically sets the element at position {@code i} to the given
152 * updated value if the current value {@code ==} the expected value.
153 *
154 * @param i the index
155 * @param expect the expected value
156 * @param update the new value
157 * @return true if successful. False return indicates that
158 * the actual value was not equal to the expected value.
159 */
160 public final boolean compareAndSet(int i, long expect, long update) {
161 return compareAndSetRaw(checkedByteOffset(i), expect, update);
162 }
163
164 private boolean compareAndSetRaw(long offset, long expect, long update) {
165 return unsafe.compareAndSwapLong(array, offset, expect, update);
166 }
167
168 /**
169 * Atomically sets the element at position {@code i} to the given
170 * updated value if the current value {@code ==} the expected value.
171 *
172 * <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
173 * and does not provide ordering guarantees, so is only rarely an
174 * appropriate alternative to {@code compareAndSet}.
175 *
176 * @param i the index
177 * @param expect the expected value
178 * @param update the new value
179 * @return true if successful
180 */
181 public final boolean weakCompareAndSet(int i, long expect, long update) {
182 return compareAndSet(i, expect, update);
183 }
184
185 /**
186 * Atomically increments by one the element at index {@code i}.
187 *
188 * @param i the index
189 * @return the previous value
190 */
191 public final long getAndIncrement(int i) {
192 return getAndAdd(i, 1);
193 }
194
195 /**
196 * Atomically decrements by one the element at index {@code i}.
197 *
198 * @param i the index
199 * @return the previous value
200 */
201 public final long getAndDecrement(int i) {
202 return getAndAdd(i, -1);
203 }
204
205 /**
206 * Atomically adds the given value to the element at index {@code i}.
207 *
208 * @param i the index
209 * @param delta the value to add
210 * @return the previous value
211 */
212 public final long getAndAdd(int i, long delta) {
213 return unsafe.getAndAddLong(array, checkedByteOffset(i), delta);
214 }
215
216 /**
217 * Atomically increments by one the element at index {@code i}.
218 *
219 * @param i the index
220 * @return the updated value
221 */
222 public final long incrementAndGet(int i) {
223 return getAndAdd(i, 1) + 1;
224 }
225
226 /**
227 * Atomically decrements by one the element at index {@code i}.
228 *
229 * @param i the index
230 * @return the updated value
231 */
232 public final long decrementAndGet(int i) {
233 return getAndAdd(i, -1) - 1;
234 }
235
236 /**
237 * Atomically adds the given value to the element at index {@code i}.
238 *
239 * @param i the index
240 * @param delta the value to add
241 * @return the updated value
242 */
243 public long addAndGet(int i, long delta) {
244 return getAndAdd(i, delta) + delta;
245 }
246
247 /**
248 * Returns the String representation of the current values of array.
249 * @return the String representation of the current values of array
250 */
251 public String toString() {
252 int iMax = array.length - 1;
253 if (iMax == -1)
254 return "[]";
255
256 StringBuilder b = new StringBuilder();
257 b.append('[');
258 for (int i = 0; ; i++) {
259 b.append(getRaw(byteOffset(i)));
260 if (i == iMax)
261 return b.append(']').toString();
262 b.append(',').append(' ');
263 }
264 }
265
266 }