Package org.apache.tomcat.util.threads

Class LimitLatch

java.lang.Object

org.apache.tomcat.util.threads.LimitLatch

public class LimitLatch
extends Object

Shared latch that allows the latch to be acquired a limited number of times after which all subsequent requests to acquire the latch will be placed in a FIFO queue until one of the shares is returned.

Constructor Summary

Constructors

Constructor	Description
LimitLatch(long limit)	Instantiates a LimitLatch object with an initial limit.

Method Summary

Modifier and Type	Method	Description
long	countDown()	Releases a shared latch, making it available for another thread to use.
void	countUpOrAwait()	Acquires a shared latch if one is available or waits for one if no shared latch is current available.
long	getCount()	Returns the current count for the latch
long	getLimit()	Obtain the current limit.
Collection<Thread>	getQueuedThreads()	Provide access to the list of threads waiting to acquire this limited shared latch.
boolean	hasQueuedThreads()	Returns true if there is at least one thread waiting to acquire the shared lock, otherwise returns false.
boolean	releaseAll()	Releases all waiting threads and causes the limit to be ignored until reset() is called.
void	reset()	Resets the latch and initializes the shared acquisition counter to zero.
void	setLimit(long limit)	Sets a new limit.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

LimitLatch

public LimitLatch(long limit)

Instantiates a LimitLatch object with an initial limit.

Parameters:

limit - - maximum number of concurrent acquisitions of this latch

Method Details

getCount

public long getCount()

Returns the current count for the latch

Returns:

the current count for latch

getLimit

public long getLimit()

Obtain the current limit.

Returns:

the limit

setLimit

public void setLimit(long limit)

Sets a new limit. If the limit is decreased there may be a period where more shares of the latch are acquired than the limit. In this case no more shares of the latch will be issued until sufficient shares have been returned to reduce the number of acquired shares of the latch to below the new limit. If the limit is increased, threads currently in the queue may not be issued one of the newly available shares until the next request is made for a latch.

Parameters:

limit - The new limit

countUpOrAwait

public void countUpOrAwait()
                    throws InterruptedException

Acquires a shared latch if one is available or waits for one if no shared latch is current available.

Throws:

InterruptedException - If the current thread is interrupted

countDown

public long countDown()

Releases a shared latch, making it available for another thread to use.

Returns:

the previous counter value

releaseAll

public boolean releaseAll()

Releases all waiting threads and causes the limit to be ignored until reset() is called.

Returns:

true if release was done

reset

public void reset()

Resets the latch and initializes the shared acquisition counter to zero.

See Also:

• releaseAll()

hasQueuedThreads

public boolean hasQueuedThreads()

Returns true if there is at least one thread waiting to acquire the shared lock, otherwise returns false.

Returns:

true if threads are waiting

getQueuedThreads

public Collection<Thread> getQueuedThreads()

Provide access to the list of threads waiting to acquire this limited shared latch.

Returns:

a collection of threads