112 lines
5.0 KiB
Java
112 lines
5.0 KiB
Java
/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* This file is available under and governed by the GNU General Public
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* License version 2 only, as published by the Free Software Foundation.
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* However, the following notice accompanied the original version of this
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* file:
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*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/publicdomain/zero/1.0/
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*/
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/**
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* A small toolkit of classes that support lock-free thread-safe
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* programming on single variables. Instances of Atomic classes
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* maintain values that are accessed and updated using methods
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* otherwise available for fields using associated atomic {@link
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* java.lang.invoke.VarHandle} operations.
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*
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* <p>Instances of classes
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* {@link java.util.concurrent.atomic.AtomicBoolean},
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* {@link java.util.concurrent.atomic.AtomicInteger},
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* {@link java.util.concurrent.atomic.AtomicLong}, and
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* {@link java.util.concurrent.atomic.AtomicReference}
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* each provide access and updates to a single variable of the
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* corresponding type. Each class also provides appropriate utility
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* methods for that type. For example, classes {@code AtomicLong} and
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* {@code AtomicInteger} provide atomic increment methods. One
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* application is to generate sequence numbers, as in:
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*
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* <pre> {@code
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* class Sequencer {
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* private final AtomicLong sequenceNumber
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* = new AtomicLong(17);
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* public long next() {
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* return sequenceNumber.getAndIncrement();
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* }
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* }}</pre>
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*
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* <p>Arbitrary transformations of the contained value are provided both
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* by low-level read-modify-write operations such as {@code compareAndSet}
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* and by higher-level methods such as {@code getAndUpdate}.
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*
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* <p>These classes are not general purpose replacements for {@code
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* java.lang.Integer} and related classes. They do <em>not</em>
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* define methods such as {@code equals}, {@code hashCode} and {@code
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* compareTo}. Because atomic variables are expected to be mutated,
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* they are poor choices for hash table keys.
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*
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* <p>The
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* {@link java.util.concurrent.atomic.AtomicIntegerArray},
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* {@link java.util.concurrent.atomic.AtomicLongArray}, and
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* {@link java.util.concurrent.atomic.AtomicReferenceArray} classes
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* further extend atomic operation support to arrays of these types.
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* These classes are also notable in providing {@code volatile} access
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* semantics for their array elements.
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*
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* <p>In addition to classes representing single values and arrays,
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* this package contains <em>Updater</em> classes that can be used to
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* obtain {@code compareAndSet} and related operations on any selected
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* {@code volatile} field of any selected class. These classes
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* predate the introduction of {@link
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* java.lang.invoke.VarHandle}, and are of more limited use.
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* {@link java.util.concurrent.atomic.AtomicReferenceFieldUpdater},
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* {@link java.util.concurrent.atomic.AtomicIntegerFieldUpdater}, and
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* {@link java.util.concurrent.atomic.AtomicLongFieldUpdater} are
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* reflection-based utilities that provide access to the associated
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* field types. These are mainly of use in atomic data structures in
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* which several {@code volatile} fields of the same node (for
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* example, the links of a tree node) are independently subject to
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* atomic updates. These classes enable greater flexibility in how
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* and when to use atomic updates, at the expense of more awkward
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* reflection-based setup, less convenient usage, and weaker
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* guarantees.
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*
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* <p>The {@link java.util.concurrent.atomic.AtomicMarkableReference}
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* class associates a single boolean with a reference. For example, this
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* bit might be used inside a data structure to mean that the object
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* being referenced has logically been deleted.
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*
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* The {@link java.util.concurrent.atomic.AtomicStampedReference}
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* class associates an integer value with a reference. This may be
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* used for example, to represent version numbers corresponding to
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* series of updates.
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*
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* @since 1.5
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*/
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package java.util.concurrent.atomic;
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