Java Reference
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can proceed. The synchronizer subclass can use
getState
,
setState
, and
com-
pareAndSetState
to examine and update the state according to its acquire and release
semantics, and informs the base class through the return status whether the attempt to acquire
or release the synchronizer was successful. For example, returning a negative value from
tryAcquireShared
indicates acquisition failure; returning zero indicates the synchron-
izer was acquired exclusively; and returning a positive value indicates the synchronizer was
acquired nonexclusively. The
tryRelease
and
tryReleaseShared
methods should
return
true
if the release may have unblocked threads attempting to acquire the synchron-
izer.
To simplify implementation of locks that support condition queues (like
ReentrantLock
),
AQS also provides machinery for constructing condition variables associated with synchron-
izers.
14.5.1. A Simple Latch
OneShotLatch
in
Listing 14.14
is a binary latch implemented using AQS. It has two pub-
lic methods,
await
and
signal
, that correspond to acquisition and release. Initially, the
latch is closed; any thread calling
await
blocks until the latch is opened. Once the latch is
opened by a call to
signal
, waiting threads are released and threads that subsequently ar-
rive at the latch will be allowed to proceed.
