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 return unsafe.getAndSetLong(this, valueOffset, newValue); 133 } 134 135 /** 136 * Atomically sets the value to the given updated value 137 * if the current value {@code ==} the expected value. 138 * 139 * @param expect the expected value 140 * @param update the new value 141 * @return true if successful. False return indicates that 142 * the actual value was not equal to the expected value. 143 */ 144 public final boolean compareAndSet(long expect, long update) { 145 return unsafe.compareAndSwapLong(this, valueOffset, expect, update); 146 } 147 148 /** 149 * Atomically sets the value to the given updated value 150 * if the current value {@code ==} the expected value. 151 * 152 * <p>May <a href="package-summary.html#Spurious">fail spuriously</a> 153 * and does not provide ordering guarantees, so is only rarely an 154 * appropriate alternative to {@code compareAndSet}. 155 * 156 * @param expect the expected value 157 * @param update the new value 158 * @return true if successful 159 */ 160 public final boolean weakCompareAndSet(long expect, long update) { 161 return unsafe.compareAndSwapLong(this, valueOffset, expect, update); 162 } 163 164 /** 165 * Atomically increments by one the current value. 166 * 167 * @return the previous value 168 */ 169 public final long getAndIncrement() { 170 return getAndAdd(1); 171 } 172 173 /** 174 * Atomically decrements by one the current value. 175 * 176 * @return the previous value 177 */ 178 public final long getAndDecrement() { 179 return getAndAdd(-1); 180 } 181 182 /** 183 * Atomically adds the given value to the current value. 184 * 185 * @param delta the value to add 186 * @return the previous value 187 */ 188 public final long getAndAdd(long delta) { 189 return unsafe.getAndAddLong(this, valueOffset, delta); 190 } 191 192 /** 193 * Atomically increments by one the current value. 194 * 195 * @return the updated value 196 */ 197 public final long incrementAndGet() { 198 return getAndAdd(1) + 1; 199 } 200 201 /** 202 * Atomically decrements by one the current value. 203 * 204 * @return the updated value 205 */ 206 public final long decrementAndGet() { 207 return getAndAdd(-1) - 1; 208 } 209 210 /** 211 * Atomically adds the given value to the current value. 212 * 213 * @param delta the value to add 214 * @return the updated value 215 */ 216 public final long addAndGet(long delta) { 217 return getAndAdd(delta) + delta; 218 } 219 220 /** 221 * Returns the String representation of the current value. 222 * @return the String representation of the current value 223 */ 224 public String toString() { 225 return Long.toString(get()); 226 } 227 228 /** 229 * Returns the value of this {@code AtomicLong} as an {@code int} 230 * after a narrowing primitive conversion. 231 * @jls 5.1.3 Narrowing Primitive Conversions 232 */ 233 public int intValue() { 234 return (int)get(); 235 } 236 237 /** 238 * Returns the value of this {@code AtomicLong} as a {@code long}. 239 */ 240 public long longValue() { 241 return get(); 242 } 243 244 /** 245 * Returns the value of this {@code AtomicLong} as a {@code float} 246 * after a widening primitive conversion. 247 * @jls 5.1.2 Widening Primitive Conversions 248 */ 249 public float floatValue() { 250 return (float)get(); 251 } 252 253 /** 254 * Returns the value of this {@code AtomicLong} as a {@code double} 255 * after a widening primitive conversion. 256 * @jls 5.1.2 Widening Primitive Conversions 257 */ 258 public double doubleValue() { 259 return (double)get(); 260 } 261 262 }