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  * A {@code long} array in which elements may be updated atomically.
  42  * See the {@link java.util.concurrent.atomic} package specification
  43  * for description of the properties of atomic variables.
  44  * @since 1.5
  45  * @author Doug Lea
  46  */
  47 public class AtomicLongArray implements java.io.Serializable {
  48     private static final long serialVersionUID = -2308431214976778248L;
  49 
  50     private static final Unsafe unsafe = Unsafe.getUnsafe();
  51     private static final int base = unsafe.arrayBaseOffset(long[].class);
  52     private static final int shift;
  53     private final long[] array;
  54 
  55     static {
  56         int scale = unsafe.arrayIndexScale(long[].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 AtomicLongArray of the given length, with all
  75      * elements initially zero.
  76      *
  77      * @param length the length of the array
  78      */
  79     public AtomicLongArray(int length) {
  80         array = new long[length];
  81     }
  82 
  83     /**
  84      * Creates a new AtomicLongArray 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 AtomicLongArray(long[] 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 long get(int i) {
 111         return getRaw(checkedByteOffset(i));
 112     }
 113 
 114     private long getRaw(long offset) {
 115         return unsafe.getLongVolatile(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, long newValue) {
 125         unsafe.putLongVolatile(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, long newValue) {
 136         unsafe.putOrderedLong(array, checkedByteOffset(i), newValue);
 137     }
 138 
 139 
 140     /**
 141      * Atomically sets the element at position {@code i} to the given value
 142      * 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 long getAndSet(int i, long newValue) {
 149         long offset = checkedByteOffset(i);
 150         while (true) {
 151             long 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, long expect, long update) {
 168         return compareAndSetRaw(checkedByteOffset(i), expect, update);
 169     }
 170 
 171     private boolean compareAndSetRaw(long offset, long expect, long update) {
 172         return unsafe.compareAndSwapLong(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, long expect, long 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 long 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 long 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 long getAndAdd(int i, long delta) {
 220         long offset = checkedByteOffset(i);
 221         while (true) {
 222             long 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 long 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 long 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 long addAndGet(int i, long delta) {
 256         long offset = checkedByteOffset(i);
 257         while (true) {
 258             long current = getRaw(offset);
 259             long 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 }