The Lock interface supports
locking disciplines that differ in semantics (reentrant, fair, etc),
and that can be used in non-block-structured contexts including
hand-over-hand and lock reordering algorithms. The main implementation
is ReentrantLock.
The ReadWriteLock interface
similarly defines locks that may be shared among readers but are
exclusive to writers. Only a single implementation, ReentrantReadWriteLock, is provided, since
it covers most standard usage contexts. But programmers may create
their own implementations to cover nonstandard requirements.
The Condition interface
describes condition variables that may be associated with Locks.
These are similar in usage to the implicit monitors accessed using
Object.wait, but offer extended capabilities.
In particular, multiple Condition objects may be associated
with a single Lock. To avoid compatibility issues, the
names of Condition methods are different from the
corresponding Object versions.
The AbstractQueuedSynchronizer
class serves as a useful superclass for defining locks and other
synchronizers that rely on queuing blocked threads. The AbstractQueuedLongSynchronizer class
provides the same functionality but extends support to 64 bits of
synchronization state. Both extend class AbstractOwnableSynchronizer, a simple
class that helps record the thread currently holding exclusive
synchronization. The LockSupport
class provides lower-level blocking and unblocking support that is
useful for those developers implementing their own customized lock
classes.
Interfaces
| Condition | Condition factors out the Object monitor
methods (wait, notify
and notifyAll) into distinct objects to
give the effect of having multiple wait-sets per object, by
combining them with the use of arbitrary Lock implementations. |
| Lock | Lock implementations provide more extensive locking
operations than can be obtained using synchronized methods
and statements. |
| ReadWriteLock | A ReadWriteLock maintains a pair of associated locks, one for read-only operations and one for writing. |
Classes
| AbstractOwnableSynchronizer | A synchronizer that may be exclusively owned by a thread. |
| AbstractQueuedLongSynchronizer | A version of AbstractQueuedSynchronizer in
which synchronization state is maintained as a long. |
| AbstractQueuedLongSynchronizer.ConditionObject | Condition implementation for a AbstractQueuedLongSynchronizer serving as the basis of a Lock implementation. |
| AbstractQueuedSynchronizer | Provides a framework for implementing blocking locks and related synchronizers (semaphores, events, etc) that rely on first-in-first-out (FIFO) wait queues. |
| AbstractQueuedSynchronizer.ConditionObject | Condition implementation for a AbstractQueuedSynchronizer serving as the basis of a Lock implementation. |
| LockSupport | Basic thread blocking primitives for creating locks and other synchronization classes. |
| ReentrantLock | A reentrant mutual exclusion Lock with the same basic
behavior and semantics as the implicit monitor lock accessed using
synchronized methods and statements, but with extended
capabilities. |
| ReentrantReadWriteLock | An implementation of ReadWriteLock supporting similar
semantics to ReentrantLock. |
| ReentrantReadWriteLock.ReadLock | The lock returned by method ReentrantReadWriteLock.readLock(). |
| ReentrantReadWriteLock.WriteLock | The lock returned by method ReentrantReadWriteLock.writeLock(). |