com.sleepycat.je.latch

Interface Latch

All Known Subinterfaces:

SharedLatch

All Known Implementing Classes:

LatchImpl, LatchWithStatsImpl, SharedLatchImpl, TimingLatch

public interface Latch

Provides exclusive (mutex-like) latching. This is implemented with Java's ReentrantLock, which is extended for a few reasons: 1) To prevent reentrant use, since latches are not used reentrantly in JE. This increases reliability by detecting accidental reentrant calls. Checks for reentrancy are unconditional, i.e., checked in production. 2) To support instrumentation for debugging (see LatchSupport). 3) Automatic use of configured latch timeout. 4) Built-in thread interrupt handling. Latches are expected to be held for short, defined periods of time. No deadlock detection is provided so it is the caller's responsibility to sequence latch acquisition in an ordered fashion to avoid deadlocks.

Method Summary

Modifier and Type	Method and Description
void	acquireExclusive() Acquires a latch for exclusive/write access.
boolean	acquireExclusiveNoWait() Acquires a latch for exclusive/write access, but do not block if it's not available.
void	clearStats() Resets collected stat values to zero.
String	debugString() Returns the same information as toString() plus all known debug info.
Thread	getExclusiveOwner() Returns the thread that currently holds the latch for exclusive access.
int	getNWaiters() Returns an estimate of the number of threads waiting.
StatGroup	getStats() Returns a stats group with information about this latch.
boolean	isExclusiveOwner() Returns true if the current thread holds this latch for exclusive/write access.
boolean	isOwner() Returns true if the current thread holds this latch.
void	release() Releases the latch.
void	releaseIfOwner() Releases the latch.
String	toString() Returns the latch name and exclusive owner info.

Method Detail

acquireExclusive

void acquireExclusive()

Acquires a latch for exclusive/write access.

Throws:

EnvironmentFailureException - if the latch is already held by the calling thread.

acquireExclusiveNoWait

boolean acquireExclusiveNoWait()

Acquires a latch for exclusive/write access, but do not block if it's not available.

Returns:

true if the latch was acquired, false if it is not available.

Throws:

EnvironmentFailureException - if the latch is already held by the calling thread.

release

void release()

Releases the latch. If there are other thread(s) waiting for the latch, they are woken up and granted the latch.

Throws:

EnvironmentFailureException - if the latch is not currently held.

releaseIfOwner

void releaseIfOwner()

Releases the latch. If there are other thread(s) waiting for the latch, one is woken up and granted the latch. If the latch was not owned by the caller, just return.

isOwner

boolean isOwner()

Returns true if the current thread holds this latch. For an exclusive latch, is equivalent to calling isExclusiveOwner().

isExclusiveOwner

boolean isExclusiveOwner()

Returns true if the current thread holds this latch for exclusive/write access.

getExclusiveOwner

Thread getExclusiveOwner()

Returns the thread that currently holds the latch for exclusive access.

getNWaiters

int getNWaiters()

Returns an estimate of the number of threads waiting.

getStats

StatGroup getStats()

Returns a stats group with information about this latch.

Throws:

EnvironmentFailureException - if stats were not requested when the latch was created. See LatchFactory.

clearStats

void clearStats()

Resets collected stat values to zero.

Throws:

EnvironmentFailureException - if stats were not requested when the latch was created. See LatchFactory.

toString

String toString()

Returns the latch name and exclusive owner info.

Overrides:

toString in class Object

debugString

String debugString()

Returns the same information as toString() plus all known debug info.