J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 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. Sun designates this |
| 7 | * particular file as subject to the "Classpath" exception as provided |
| 8 | * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 21 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 22 | * have any 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 array of object references in which elements may be updated |
| 42 | * atomically. 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 | * @param <E> The base class of elements held in this array |
| 48 | */ |
| 49 | public class AtomicReferenceArray<E> implements java.io.Serializable { |
| 50 | private static final long serialVersionUID = -6209656149925076980L; |
| 51 | |
| 52 | private static final Unsafe unsafe = Unsafe.getUnsafe(); |
| 53 | private static final int base = unsafe.arrayBaseOffset(Object[].class); |
| 54 | private static final int scale = unsafe.arrayIndexScale(Object[].class); |
| 55 | private final Object[] array; |
| 56 | |
| 57 | private long rawIndex(int i) { |
| 58 | if (i < 0 || i >= array.length) |
| 59 | throw new IndexOutOfBoundsException("index " + i); |
| 60 | return base + i * scale; |
| 61 | } |
| 62 | |
| 63 | /** |
| 64 | * Creates a new AtomicReferenceArray of given length. |
| 65 | * @param length the length of the array |
| 66 | */ |
| 67 | public AtomicReferenceArray(int length) { |
| 68 | array = new Object[length]; |
| 69 | // must perform at least one volatile write to conform to JMM |
| 70 | if (length > 0) |
| 71 | unsafe.putObjectVolatile(array, rawIndex(0), null); |
| 72 | } |
| 73 | |
| 74 | /** |
| 75 | * Creates a new AtomicReferenceArray with the same length as, and |
| 76 | * all elements copied from, the given array. |
| 77 | * |
| 78 | * @param array the array to copy elements from |
| 79 | * @throws NullPointerException if array is null |
| 80 | */ |
| 81 | public AtomicReferenceArray(E[] array) { |
| 82 | if (array == null) |
| 83 | throw new NullPointerException(); |
| 84 | int length = array.length; |
| 85 | this.array = new Object[length]; |
| 86 | if (length > 0) { |
| 87 | int last = length-1; |
| 88 | for (int i = 0; i < last; ++i) |
| 89 | this.array[i] = array[i]; |
| 90 | // Do the last write as volatile |
| 91 | E e = array[last]; |
| 92 | unsafe.putObjectVolatile(this.array, rawIndex(last), e); |
| 93 | } |
| 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 E get(int i) { |
| 112 | return (E) unsafe.getObjectVolatile(array, rawIndex(i)); |
| 113 | } |
| 114 | |
| 115 | /** |
| 116 | * Sets the element at position {@code i} to the given value. |
| 117 | * |
| 118 | * @param i the index |
| 119 | * @param newValue the new value |
| 120 | */ |
| 121 | public final void set(int i, E newValue) { |
| 122 | unsafe.putObjectVolatile(array, rawIndex(i), newValue); |
| 123 | } |
| 124 | |
| 125 | /** |
| 126 | * Eventually sets the element at position {@code i} to the given value. |
| 127 | * |
| 128 | * @param i the index |
| 129 | * @param newValue the new value |
| 130 | * @since 1.6 |
| 131 | */ |
| 132 | public final void lazySet(int i, E newValue) { |
| 133 | unsafe.putOrderedObject(array, rawIndex(i), newValue); |
| 134 | } |
| 135 | |
| 136 | |
| 137 | /** |
| 138 | * Atomically sets the element at position {@code i} to the given |
| 139 | * value and returns the old value. |
| 140 | * |
| 141 | * @param i the index |
| 142 | * @param newValue the new value |
| 143 | * @return the previous value |
| 144 | */ |
| 145 | public final E getAndSet(int i, E newValue) { |
| 146 | while (true) { |
| 147 | E current = get(i); |
| 148 | if (compareAndSet(i, current, newValue)) |
| 149 | return current; |
| 150 | } |
| 151 | } |
| 152 | |
| 153 | /** |
| 154 | * Atomically sets the element at position {@code i} to the given |
| 155 | * updated value if the current value {@code ==} the expected value. |
| 156 | * @param i the index |
| 157 | * @param expect the expected value |
| 158 | * @param update the new value |
| 159 | * @return true if successful. False return indicates that |
| 160 | * the actual value was not equal to the expected value. |
| 161 | */ |
| 162 | public final boolean compareAndSet(int i, E expect, E update) { |
| 163 | return unsafe.compareAndSwapObject(array, rawIndex(i), |
| 164 | expect, update); |
| 165 | } |
| 166 | |
| 167 | /** |
| 168 | * Atomically sets the element at position {@code i} to the given |
| 169 | * updated value if the current value {@code ==} the expected value. |
| 170 | * |
| 171 | * <p>May <a href="package-summary.html#Spurious">fail spuriously</a> |
| 172 | * and does not provide ordering guarantees, so is only rarely an |
| 173 | * appropriate alternative to {@code compareAndSet}. |
| 174 | * |
| 175 | * @param i the index |
| 176 | * @param expect the expected value |
| 177 | * @param update the new value |
| 178 | * @return true if successful. |
| 179 | */ |
| 180 | public final boolean weakCompareAndSet(int i, E expect, E update) { |
| 181 | return compareAndSet(i, expect, update); |
| 182 | } |
| 183 | |
| 184 | /** |
| 185 | * Returns the String representation of the current values of array. |
| 186 | * @return the String representation of the current values of array. |
| 187 | */ |
| 188 | public String toString() { |
| 189 | if (array.length > 0) // force volatile read |
| 190 | get(0); |
| 191 | return Arrays.toString(array); |
| 192 | } |
| 193 | |
| 194 | } |