java.util.concurrent.atomic.package-info Maven / Gradle / Ivy
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/*
* This file is available under and governed by the GNU General Public
* License version 2 only, as published by the Free Software Foundation.
* However, the following notice accompanied the original version of this
* file:
*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
/**
* A small toolkit of classes that support lock-free thread-safe
* programming on single variables. Instances of Atomic classes
* maintain values that are accessed and updated using methods
* otherwise available for fields using associated atomic {@link
* java.lang.invoke.VarHandle} operations.
*
* Instances of classes
* {@link java.util.concurrent.atomic.AtomicBoolean},
* {@link java.util.concurrent.atomic.AtomicInteger},
* {@link java.util.concurrent.atomic.AtomicLong}, and
* {@link java.util.concurrent.atomic.AtomicReference}
* each provide access and updates to a single variable of the
* corresponding type. Each class also provides appropriate utility
* methods for that type. For example, classes {@code AtomicLong} and
* {@code AtomicInteger} provide atomic increment methods. One
* application is to generate sequence numbers, as in:
*
*
{@code
* class Sequencer {
* private final AtomicLong sequenceNumber
* = new AtomicLong(17);
* public long next() {
* return sequenceNumber.getAndIncrement();
* }
* }}
*
* Arbitrary transformations of the contained value are provided both
* by low-level read-modify-write operations such as {@code compareAndSet}
* and by higher-level methods such as {@code getAndUpdate}.
*
*
These classes are not general purpose replacements for {@code
* java.lang.Integer} and related classes. They do not
* define methods such as {@code equals}, {@code hashCode} and {@code
* compareTo}. Because atomic variables are expected to be mutated,
* they are poor choices for hash table keys.
*
*
The
* {@link java.util.concurrent.atomic.AtomicIntegerArray},
* {@link java.util.concurrent.atomic.AtomicLongArray}, and
* {@link java.util.concurrent.atomic.AtomicReferenceArray} classes
* further extend atomic operation support to arrays of these types.
* These classes are also notable in providing {@code volatile} access
* semantics for their array elements.
*
*
In addition to classes representing single values and arrays,
* this package contains Updater classes that can be used to
* obtain {@code compareAndSet} and related operations on any selected
* {@code volatile} field of any selected class. These classes
* predate the introduction of {@link
* java.lang.invoke.VarHandle}, and are of more limited use.
* {@link java.util.concurrent.atomic.AtomicReferenceFieldUpdater},
* {@link java.util.concurrent.atomic.AtomicIntegerFieldUpdater}, and
* {@link java.util.concurrent.atomic.AtomicLongFieldUpdater} are
* reflection-based utilities that provide access to the associated
* field types. These are mainly of use in atomic data structures in
* which several {@code volatile} fields of the same node (for
* example, the links of a tree node) are independently subject to
* atomic updates. These classes enable greater flexibility in how
* and when to use atomic updates, at the expense of more awkward
* reflection-based setup, less convenient usage, and weaker
* guarantees.
*
*
The {@link java.util.concurrent.atomic.AtomicMarkableReference}
* class associates a single boolean with a reference. For example, this
* bit might be used inside a data structure to mean that the object
* being referenced has logically been deleted.
*
* The {@link java.util.concurrent.atomic.AtomicStampedReference}
* class associates an integer value with a reference. This may be
* used for example, to represent version numbers corresponding to
* series of updates.
*
* @since 1.5
*/
package java.util.concurrent.atomic;