AtomicLongArray.java revision 51b1b6997fd3f980076b8081f7f1165ccc2a4008 
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
36package java.util.concurrent.atomic;
37import sun.misc.Unsafe;
38import 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 */
47public 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}
285