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
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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 /**
37 * A small toolkit of classes that support lock-free thread-safe
38 * programming on single variables. Instances of Atomic classes
39 * maintain values that are accessed and updated using methods
40 * otherwise available for fields using associated atomic {@link
41 * java.lang.invoke.VarHandle} operations.
42 *
43 * <p>Instances of classes
44 * {@link java.util.concurrent.atomic.AtomicBoolean},
45 * {@link java.util.concurrent.atomic.AtomicInteger},
46 * {@link java.util.concurrent.atomic.AtomicLong}, and
47 * {@link java.util.concurrent.atomic.AtomicReference}
48 * each provide access and updates to a single variable of the
49 * corresponding type. Each class also provides appropriate utility
50 * methods for that type. For example, classes {@code AtomicLong} and
51 * {@code AtomicInteger} provide atomic increment methods. One
52 * application is to generate sequence numbers, as in:
53 *
54 * <pre> {@code
55 * class Sequencer {
56 * private final AtomicLong sequenceNumber
57 * = new AtomicLong(0);
58 * public long next() {
59 * return sequenceNumber.getAndIncrement();
60 * }
61 * }}</pre>
62 *
63 * <p>Arbitrary transformations of the contained value are provided both
64 * by low-level read-modify-write operations such as {@code compareAndSet}
65 * and by higher-level methods such as {@code getAndUpdate}.
66 *
67 * <p>These classes are not general purpose replacements for {@code
68 * java.lang.Integer} and related classes. They do <em>not</em>
69 * define methods such as {@code equals}, {@code hashCode} and {@code
70 * compareTo}. Because atomic variables are expected to be mutated,
71 * they are poor choices for hash table keys.
72 *
73 * <p>The
74 * {@link java.util.concurrent.atomic.AtomicIntegerArray},
75 * {@link java.util.concurrent.atomic.AtomicLongArray}, and
76 * {@link java.util.concurrent.atomic.AtomicReferenceArray} classes
77 * further extend atomic operation support to arrays of these types.
78 * These classes are also notable in providing {@code volatile} access
79 * semantics for their array elements.
80 *
81 * <p>In addition to classes representing single values and arrays,
82 * this package contains <em>Updater</em> classes that can be used to
83 * obtain {@code compareAndSet} and related operations on any selected
84 * {@code volatile} field of any selected class. These classes
85 * predate the introduction of {@link
86 * java.lang.invoke.VarHandle}, and are of more limited use.
87 * {@link java.util.concurrent.atomic.AtomicReferenceFieldUpdater},
88 * {@link java.util.concurrent.atomic.AtomicIntegerFieldUpdater}, and
89 * {@link java.util.concurrent.atomic.AtomicLongFieldUpdater} are
90 * reflection-based utilities that provide access to the associated
91 * field types. These are mainly of use in atomic data structures in
92 * which several {@code volatile} fields of the same node (for
93 * example, the links of a tree node) are independently subject to
94 * atomic updates. These classes enable greater flexibility in how
95 * and when to use atomic updates, at the expense of more awkward
96 * reflection-based setup, less convenient usage, and weaker
97 * guarantees.
98 *
99 * <p>The {@link java.util.concurrent.atomic.AtomicMarkableReference}
100 * class associates a single boolean with a reference. For example, this
101 * bit might be used inside a data structure to mean that the object
102 * being referenced has logically been deleted.
103 *
104 * The {@link java.util.concurrent.atomic.AtomicStampedReference}
105 * class associates an integer value with a reference. This may be
106 * used for example, to represent version numbers corresponding to
107 * series of updates.
108 *
109 * @since 1.5
110 */
111 package java.util.concurrent.atomic;