net.sf.asyncobjects.util
Interface ASemaphore

All Superinterfaces:

AsyncObject

All Known Implementing Classes:

Semaphore

public interface ASemaphore
extends AsyncObject

This is an asynchronous version of Semaphore. It maintain internal balance of permits. The method release(int) increases the amount of permits and the method acquire(int) reduces the amount. However the method acquire reduces amount of permits and resolves its result promise only when amount of permits will be at least zero after substracting the permits.

The method drainPermits() resets the amount of permits to zero when all previously enqueued acquire(int) completed.

Ivocations of the methods acquire(int) and drainPermits() are ordered. the later invocation will not be executed until the first one is complete. In contrast to it, the release(int) methods are not queued. They are executed as soon as they are received.

Author:

const

Method Summary

Promise<Void>	acquire()
Promise<Void>	acquire(int number) Aquiree a number of permits
Promise<Integer>	availablePermits() This is amount of permits that are released but have not yet been acquired with a acquire(int) call.
Promise<Integer>	drainPermits() Drain all available permits.
Promise<Integer>	permitsBalance()
void	release() Release a permit
void	release(int number) Release a number of permits

Methods inherited from interface net.sf.asyncobjects.AsyncObject

dereference, isImmediate

Method Detail

acquire

Promise<Void> acquire()

Returns:

when aquired one permit

acquire

Promise<Void> acquire(int number)

Aquiree a number of permits

Parameters:

number - amount of permits to aquired

Returns:

when permits are aquired

release

void release()

Release a permit

release

void release(int number)

Release a number of permits

Parameters:

number - a number of permits

availablePermits

Promise<Integer> availablePermits()

This is amount of permits that are released but have not yet been acquired with a acquire(int) call. If there are pending acquire(int) call, this could happen due to several reasons:

• the acquire(int) call could be not yet awaken.
• the argument of acquire(int) is greater than amount of available permits.

Returns:

amount of currently available permits.

permitsBalance

Promise<Integer> permitsBalance()

Returns:

return an permits balance. The sum of permits requested by pending acquire(int) calls is substracted from available permits.

drainPermits

Promise<Integer> drainPermits()

Drain all available permits. Note that this method waits until at least zero permits available. If less than zero permits available, the method blocks.

Returns:

amount of permits that were available.