java.util.concurrent.atomic
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 atomicVarHandle operations.
Instances of classes
AtomicBoolean,
AtomicInteger,
AtomicLong, and
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 AtomicLong and
AtomicInteger provide atomic increment methods. One
application is to generate sequence numbers, as in:
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 compareAndSet
and by higher-level methods such as getAndUpdate.
These classes are not general purpose replacements for java.lang.Integer and related classes. They do not
define methods such as equals, hashCode and compareTo. Because atomic variables are expected to be mutated,
they are poor choices for hash table keys.
The
AtomicIntegerArray,
AtomicLongArray, and
AtomicReferenceArray classes
further extend atomic operation support to arrays of these types.
These classes are also notable in providing 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 compareAndSet and related operations on any selected
volatile field of any selected class. These classes
predate the introduction of VarHandle, and are of more limited use.
AtomicReferenceFieldUpdater,
AtomicIntegerFieldUpdater, and
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 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 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 AtomicStampedReference
class associates an integer value with a reference. This may be
used for example, to represent version numbers corresponding to
series of updates.
Classes
| AtomicBoolean |
A boolean value that may be updated atomically.
|
| AtomicInteger |
An int value that may be updated atomically.
|
| AtomicIntegerArray |
An int array in which elements may be updated atomically.
|
| AtomicIntegerFieldUpdater<T> |
A reflection-based utility that enables atomic updates to
designated volatile int fields of designated classes.
|
| AtomicLong |
A long value that may be updated atomically.
|
| AtomicLongArray |
A long array in which elements may be updated atomically.
|
| AtomicLongFieldUpdater<T> |
A reflection-based utility that enables atomic updates to
designated volatile long fields of designated classes.
|
| AtomicMarkableReference<V> |
An AtomicMarkableReference maintains an object reference
along with a mark bit, that can be updated atomically.
|
| AtomicReference<V> | An object reference that may be updated atomically. |
| AtomicReferenceArray<E> | An array of object references in which elements may be updated atomically. |
| AtomicReferenceFieldUpdater<T, V> |
A reflection-based utility that enables atomic updates to
designated volatile reference fields of designated
classes.
|
| AtomicStampedReference<V> |
An AtomicStampedReference maintains an object reference
along with an integer "stamp", that can be updated atomically.
|
| DoubleAccumulator |
One or more variables that together maintain a running double
value updated using a supplied function.
|
| DoubleAdder |
One or more variables that together maintain an initially zero
double sum.
|
| LongAccumulator |
One or more variables that together maintain a running long
value updated using a supplied function.
|
| LongAdder |
One or more variables that together maintain an initially zero
long sum.
|