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/licenses/publicdomain 34 */ 35 36 package java.util.concurrent.atomic; 37 import sun.misc.Unsafe; 38 import java.util.*; 39 40 /** 41 * An {@code int} array in which elements may be updated atomically. 42 * See the {@link java.util.concurrent.atomic} package 43 * specification for description of the properties of atomic 44 * variables. 45 * @since 1.5 46 * @author Doug Lea 47 */ 48 public class AtomicIntegerArray implements java.io.Serializable { 49 private static final long serialVersionUID = 2862133569453604235L; 50 51 private static final Unsafe unsafe = Unsafe.getUnsafe(); 52 private static final int base = unsafe.arrayBaseOffset(int[].class); 53 private static final int shift; 54 private final int[] array; 55 56 static { 57 int scale = unsafe.arrayIndexScale(int[].class); 58 if ((scale & (scale - 1)) != 0) 59 throw new Error("data type scale not a power of two"); 60 shift = 31 - Integer.numberOfLeadingZeros(scale); 61 } 62 63 private long checkedByteOffset(int i) { 64 if (i < 0 || i >= array.length) 65 throw new IndexOutOfBoundsException("index " + i); 66 67 return byteOffset(i); 68 } 69 70 private static long byteOffset(int i) { 71 return ((long) i << shift) + base; 72 } 73 74 /** 75 * Creates a new AtomicIntegerArray of the given length, with all 76 * elements initially zero. 77 * 78 * @param length the length of the array 79 */ 80 public AtomicIntegerArray(int length) { 81 array = new int[length]; 82 } 83 84 /** 85 * Creates a new AtomicIntegerArray with the same length as, and 86 * all elements copied from, the given array. 87 * 88 * @param array the array to copy elements from 89 * @throws NullPointerException if array is null 90 */ 91 public AtomicIntegerArray(int[] array) { 92 // Visibility guaranteed by final field guarantees 93 this.array = array.clone(); 94 } 95 96 /** 97 * Returns the length of the array. 98 * 99 * @return the length of the array 100 */ 101 public final int length() { 102 return array.length; 103 } 104 105 /** 106 * Gets the current value at position {@code i}. 107 * 108 * @param i the index 109 * @return the current value 110 */ 111 public final int get(int i) { 112 return getRaw(checkedByteOffset(i)); 113 } 114 115 private int getRaw(long offset) { 116 return unsafe.getIntVolatile(array, offset); 117 } 118 119 /** 120 * Sets the element at position {@code i} to the given value. 121 * 122 * @param i the index 123 * @param newValue the new value 124 */ 125 public final void set(int i, int newValue) { 126 unsafe.putIntVolatile(array, checkedByteOffset(i), newValue); 127 } 128 129 /** 130 * Eventually sets the element at position {@code i} to the given value. 131 * 132 * @param i the index 133 * @param newValue the new value 134 * @since 1.6 135 */ 136 public final void lazySet(int i, int newValue) { 137 unsafe.putOrderedInt(array, checkedByteOffset(i), newValue); 138 } 139 140 /** 141 * Atomically sets the element at position {@code i} to the given 142 * value and returns the old value. 143 * 144 * @param i the index 145 * @param newValue the new value 146 * @return the previous value 147 */ 148 public final int getAndSet(int i, int newValue) { 149 long offset = checkedByteOffset(i); 150 while (true) { 151 int current = getRaw(offset); 152 if (compareAndSetRaw(offset, current, newValue)) 153 return current; 154 } 155 } 156 157 /** 158 * Atomically sets the element at position {@code i} to the given 159 * updated value if the current value {@code ==} the expected value. 160 * 161 * @param i the index 162 * @param expect the expected value 163 * @param update the new value 164 * @return true if successful. False return indicates that 165 * the actual value was not equal to the expected value. 166 */ 167 public final boolean compareAndSet(int i, int expect, int update) { 168 return compareAndSetRaw(checkedByteOffset(i), expect, update); 169 } 170 171 private boolean compareAndSetRaw(long offset, int expect, int update) { 172 return unsafe.compareAndSwapInt(array, offset, expect, update); 173 } 174 175 /** 176 * Atomically sets the element at position {@code i} to the given 177 * updated value if the current value {@code ==} the expected value. 178 * 179 * <p>May <a href="package-summary.html#Spurious">fail spuriously</a> 180 * and does not provide ordering guarantees, so is only rarely an 181 * appropriate alternative to {@code compareAndSet}. 182 * 183 * @param i the index 184 * @param expect the expected value 185 * @param update the new value 186 * @return true if successful. 187 */ 188 public final boolean weakCompareAndSet(int i, int expect, int update) { 189 return compareAndSet(i, expect, update); 190 } 191 192 /** 193 * Atomically increments by one the element at index {@code i}. 194 * 195 * @param i the index 196 * @return the previous value 197 */ 198 public final int getAndIncrement(int i) { 199 return getAndAdd(i, 1); 200 } 201 202 /** 203 * Atomically decrements by one the element at index {@code i}. 204 * 205 * @param i the index 206 * @return the previous value 207 */ 208 public final int getAndDecrement(int i) { 209 return getAndAdd(i, -1); 210 } 211 212 /** 213 * Atomically adds the given value to the element at index {@code i}. 214 * 215 * @param i the index 216 * @param delta the value to add 217 * @return the previous value 218 */ 219 public final int getAndAdd(int i, int delta) { 220 long offset = checkedByteOffset(i); 221 while (true) { 222 int current = getRaw(offset); 223 if (compareAndSetRaw(offset, current, current + delta)) 224 return current; 225 } 226 } 227 228 /** 229 * Atomically increments by one the element at index {@code i}. 230 * 231 * @param i the index 232 * @return the updated value 233 */ 234 public final int incrementAndGet(int i) { 235 return addAndGet(i, 1); 236 } 237 238 /** 239 * Atomically decrements by one the element at index {@code i}. 240 * 241 * @param i the index 242 * @return the updated value 243 */ 244 public final int decrementAndGet(int i) { 245 return addAndGet(i, -1); 246 } 247 248 /** 249 * Atomically adds the given value to the element at index {@code i}. 250 * 251 * @param i the index 252 * @param delta the value to add 253 * @return the updated value 254 */ 255 public final int addAndGet(int i, int delta) { 256 long offset = checkedByteOffset(i); 257 while (true) { 258 int current = getRaw(offset); 259 int next = current + delta; 260 if (compareAndSetRaw(offset, current, next)) 261 return next; 262 } 263 } 264 265 /** 266 * Returns the String representation of the current values of array. 267 * @return the String representation of the current values of array 268 */ 269 public String toString() { 270 int iMax = array.length - 1; 271 if (iMax == -1) 272 return "[]"; 273 274 StringBuilder b = new StringBuilder(); 275 b.append('['); 276 for (int i = 0; ; i++) { 277 b.append(getRaw(byteOffset(i))); 278 if (i == iMax) 279 return b.append(']').toString(); 280 b.append(',').append(' '); 281 } 282 } 283 284 } --- EOF ---