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 }