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} value that may be updated atomically. See the 41 * {@link java.util.concurrent.atomic} package specification for 42 * description of the properties of atomic variables. An 43 * {@code AtomicLong} is used in applications such as atomically 44 * incremented sequence numbers, and cannot be used as a replacement 45 * for a {@link java.lang.Long}. However, this class does extend 46 * {@code Number} to allow uniform access by tools and utilities that 47 * deal with numerically-based classes. 48 * 49 * @since 1.5 50 * @author Doug Lea 51 */ 52 public class AtomicLong extends Number implements java.io.Serializable { 53 private static final long serialVersionUID = 1927816293512124184L; 54 55 // setup to use Unsafe.compareAndSwapLong for updates 56 private static final Unsafe unsafe = Unsafe.getUnsafe(); 57 private static final long valueOffset; 58 59 /** 60 * Records whether the underlying JVM supports lockless 61 * compareAndSwap for longs. While the Unsafe.compareAndSwapLong 62 * method works in either case, some constructions should be 63 * handled at Java level to avoid locking user-visible locks. 64 */ 65 static final boolean VM_SUPPORTS_LONG_CAS = VMSupportsCS8(); 66 67 /** 68 * Returns whether underlying JVM supports lockless CompareAndSet 69 * for longs. Called only once and cached in VM_SUPPORTS_LONG_CAS. 70 */ 71 private static native boolean VMSupportsCS8(); 72 73 static { 74 try { 75 valueOffset = unsafe.objectFieldOffset 76 (AtomicLong.class.getDeclaredField("value")); 77 } catch (Exception ex) { throw new Error(ex); } 78 } 79 80 private volatile long value; 81 82 /** 83 * Creates a new AtomicLong with the given initial value. 84 * 85 * @param initialValue the initial value 86 */ 87 public AtomicLong(long initialValue) { 88 value = initialValue; 89 } 90 91 /** 92 * Creates a new AtomicLong with initial value {@code 0}. 93 */ 94 public AtomicLong() { 95 } 96 97 /** 98 * Gets the current value. 99 * 100 * @return the current value 101 */ 102 public final long get() { 103 return value; 104 } 105 106 /** 107 * Sets to the given value. 108 * 109 * @param newValue the new value 110 */ 111 public final void set(long newValue) { 112 value = newValue; 113 } 114 115 /** 116 * Eventually sets to the given value. 117 * 118 * @param newValue the new value 119 * @since 1.6 120 */ 121 public final void lazySet(long newValue) { 122 unsafe.putOrderedLong(this, valueOffset, newValue); 123 } 124 125 /** 126 * Atomically sets to the given value and returns the old value. 127 * 128 * @param newValue the new value 129 * @return the previous value 130 */ 131 public final long getAndSet(long newValue) { 132 while (true) { 133 long current = get(); 134 if (compareAndSet(current, newValue)) 135 return current; 136 } 137 } 138 139 /** 140 * Atomically sets the value to the given updated value 141 * if the current value {@code ==} the expected value. 142 * 143 * @param expect the expected value 144 * @param update the new value 145 * @return true if successful. False return indicates that 146 * the actual value was not equal to the expected value. 147 */ 148 public final boolean compareAndSet(long expect, long update) { 149 return unsafe.compareAndSwapLong(this, valueOffset, expect, update); 150 } 151 152 /** 153 * Atomically sets the value to the given updated value 154 * if the current value {@code ==} the expected value. 155 * 156 * <p>May <a href="package-summary.html#Spurious">fail spuriously</a> 157 * and does not provide ordering guarantees, so is only rarely an 158 * appropriate alternative to {@code compareAndSet}. 159 * 160 * @param expect the expected value 161 * @param update the new value 162 * @return true if successful. 163 */ 164 public final boolean weakCompareAndSet(long expect, long update) { 165 return unsafe.compareAndSwapLong(this, valueOffset, expect, update); 166 } 167 168 /** 169 * Atomically increments by one the current value. 170 * 171 * @return the previous value 172 */ 173 public final long getAndIncrement() { 174 while (true) { 175 long current = get(); 176 long next = current + 1; 177 if (compareAndSet(current, next)) 178 return current; 179 } 180 } 181 182 /** 183 * Atomically decrements by one the current value. 184 * 185 * @return the previous value 186 */ 187 public final long getAndDecrement() { 188 while (true) { 189 long current = get(); 190 long next = current - 1; 191 if (compareAndSet(current, next)) 192 return current; 193 } 194 } 195 196 /** 197 * Atomically adds the given value to the current value. 198 * 199 * @param delta the value to add 200 * @return the previous value 201 */ 202 public final long getAndAdd(long delta) { 203 while (true) { 204 long current = get(); 205 long next = current + delta; 206 if (compareAndSet(current, next)) 207 return current; 208 } 209 } 210 211 /** 212 * Atomically increments by one the current value. 213 * 214 * @return the updated value 215 */ 216 public final long incrementAndGet() { 217 for (;;) { 218 long current = get(); 219 long next = current + 1; 220 if (compareAndSet(current, next)) 221 return next; 222 } 223 } 224 225 /** 226 * Atomically decrements by one the current value. 227 * 228 * @return the updated value 229 */ 230 public final long decrementAndGet() { 231 for (;;) { 232 long current = get(); 233 long next = current - 1; 234 if (compareAndSet(current, next)) 235 return next; 236 } 237 } 238 239 /** 240 * Atomically adds the given value to the current value. 241 * 242 * @param delta the value to add 243 * @return the updated value 244 */ 245 public final long addAndGet(long delta) { 246 for (;;) { 247 long current = get(); 248 long next = current + delta; 249 if (compareAndSet(current, next)) 250 return next; 251 } 252 } 253 254 /** 255 * Returns the String representation of the current value. 256 * @return the String representation of the current value. 257 */ 258 public String toString() { 259 return Long.toString(get()); 260 } 261 262 263 public int intValue() { 264 return (int)get(); 265 } 266 267 public long longValue() { 268 return get(); 269 } 270 271 public float floatValue() { 272 return (float)get(); 273 } 274 275 public double doubleValue() { 276 return (double)get(); 277 } 278 279 }