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 * An {@code int} array in which elements may be updated atomically.
41 * See the {@link java.util.concurrent.atomic} package
42 * specification for description of the properties of atomic
43 * variables.
44 * @since 1.5
45 * @author Doug Lea
46 */
47 public class AtomicIntegerArray implements java.io.Serializable {
48 private static final long serialVersionUID = 2862133569453604235L;
49
50 private static final Unsafe unsafe = Unsafe.getUnsafe();
51 private static final int base = unsafe.arrayBaseOffset(int[].class);
52 private static final int shift;
53 private final int[] array;
54
55 static {
56 int scale = unsafe.arrayIndexScale(int[].class);
57 if ((scale & (scale - 1)) != 0)
58 throw new Error("data type scale not a power of two");
59 shift = 31 - Integer.numberOfLeadingZeros(scale);
60 }
61
62 private long checkedByteOffset(int i) {
63 if (i < 0 || i >= array.length)
64 throw new IndexOutOfBoundsException("index " + i);
65
66 return byteOffset(i);
67 }
68
69 private static long byteOffset(int i) {
70 return ((long) i << shift) + base;
71 }
72
73 /**
74 * Creates a new AtomicIntegerArray of the given length, with all
75 * elements initially zero.
76 *
77 * @param length the length of the array
78 */
79 public AtomicIntegerArray(int length) {
80 array = new int[length];
81 }
82
83 /**
84 * Creates a new AtomicIntegerArray with the same length as, and
85 * all elements copied from, the given array.
86 *
87 * @param array the array to copy elements from
88 * @throws NullPointerException if array is null
89 */
90 public AtomicIntegerArray(int[] array) {
91 // Visibility guaranteed by final field guarantees
92 this.array = array.clone();
93 }
94
95 /**
96 * Returns the length of the array.
97 *
98 * @return the length of the array
99 */
100 public final int length() {
101 return array.length;
102 }
103
104 /**
105 * Gets the current value at position {@code i}.
106 *
107 * @param i the index
108 * @return the current value
109 */
110 public final int get(int i) {
111 return getRaw(checkedByteOffset(i));
112 }
113
114 private int getRaw(long offset) {
115 return unsafe.getIntVolatile(array, offset);
116 }
117
118 /**
119 * Sets the element at position {@code i} to the given value.
120 *
121 * @param i the index
122 * @param newValue the new value
123 */
124 public final void set(int i, int newValue) {
125 unsafe.putIntVolatile(array, checkedByteOffset(i), newValue);
126 }
127
128 /**
129 * Eventually sets the element at position {@code i} to the given value.
130 *
131 * @param i the index
132 * @param newValue the new value
133 * @since 1.6
134 */
135 public final void lazySet(int i, int newValue) {
136 unsafe.putOrderedInt(array, checkedByteOffset(i), newValue);
137 }
138
139 /**
140 * Atomically sets the element at position {@code i} to the given
141 * value and returns the old value.
142 *
143 * @param i the index
144 * @param newValue the new value
145 * @return the previous value
146 */
147 public final int getAndSet(int i, int newValue) {
148 return unsafe.getAndSetInt(array, checkedByteOffset(i), newValue);
149 }
150
151 /**
152 * Atomically sets the element at position {@code i} to the given
153 * updated value if the current value {@code ==} the expected value.
154 *
155 * @param i the index
156 * @param expect the expected value
157 * @param update the new value
158 * @return true if successful. False return indicates that
159 * the actual value was not equal to the expected value.
160 */
161 public final boolean compareAndSet(int i, int expect, int update) {
162 return compareAndSetRaw(checkedByteOffset(i), expect, update);
163 }
164
165 private boolean compareAndSetRaw(long offset, int expect, int update) {
166 return unsafe.compareAndSwapInt(array, offset, expect, update);
167 }
168
169 /**
170 * Atomically sets the element at position {@code i} to the given
171 * updated value if the current value {@code ==} the expected value.
172 *
173 * <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
174 * and does not provide ordering guarantees, so is only rarely an
175 * appropriate alternative to {@code compareAndSet}.
176 *
177 * @param i the index
178 * @param expect the expected value
179 * @param update the new value
180 * @return true if successful
181 */
182 public final boolean weakCompareAndSet(int i, int expect, int update) {
183 return compareAndSet(i, expect, update);
184 }
185
186 /**
187 * Atomically increments by one the element at index {@code i}.
188 *
189 * @param i the index
190 * @return the previous value
191 */
192 public final int getAndIncrement(int i) {
193 return getAndAdd(i, 1);
194 }
195
196 /**
197 * Atomically decrements by one the element at index {@code i}.
198 *
199 * @param i the index
200 * @return the previous value
201 */
202 public final int getAndDecrement(int i) {
203 return getAndAdd(i, -1);
204 }
205
206 /**
207 * Atomically adds the given value to the element at index {@code i}.
208 *
209 * @param i the index
210 * @param delta the value to add
211 * @return the previous value
212 */
213 public final int getAndAdd(int i, int delta) {
214 return unsafe.getAndAddInt(array, checkedByteOffset(i), delta);
215 }
216
217 /**
218 * Atomically increments by one the element at index {@code i}.
219 *
220 * @param i the index
221 * @return the updated value
222 */
223 public final int incrementAndGet(int i) {
224 return getAndAdd(i, 1) + 1;
225 }
226
227 /**
228 * Atomically decrements by one the element at index {@code i}.
229 *
230 * @param i the index
231 * @return the updated value
232 */
233 public final int decrementAndGet(int i) {
234 return getAndAdd(i, -1) - 1;
235 }
236
237 /**
238 * Atomically adds the given value to the element at index {@code i}.
239 *
240 * @param i the index
241 * @param delta the value to add
242 * @return the updated value
243 */
244 public final int addAndGet(int i, int delta) {
245 return getAndAdd(i, delta) + delta;
246 }
247
248 /**
249 * Returns the String representation of the current values of array.
250 * @return the String representation of the current values of array
251 */
252 public String toString() {
253 int iMax = array.length - 1;
254 if (iMax == -1)
255 return "[]";
256
257 StringBuilder b = new StringBuilder();
258 b.append('[');
259 for (int i = 0; ; i++) {
260 b.append(getRaw(byteOffset(i)));
261 if (i == iMax)
262 return b.append(']').toString();
263 b.append(',').append(' ');
264 }
265 }
266
267 }