org.redisson.api

Interface RSemaphore

All Superinterfaces:

RExpirable, RExpirableAsync, RObject, RObjectAsync, RSemaphoreAsync

All Known Implementing Classes:

RedissonQueueSemaphore, RedissonSemaphore

public interface RSemaphore
extends RExpirable, RSemaphoreAsync

Distributed and concurrent implementation of Semaphore.

Works in non-fair mode. Therefore order of acquiring is unpredictable.

Author:

Nikita Koksharov

Method Summary

Modifier and Type	Method and Description
void	acquire() Acquires a permit from this semaphore, blocking until one is available, or the thread is interrupted.
void	acquire(int permits) Acquires the given number of permits from this semaphore, blocking until all are available, or the thread is interrupted.
int	availablePermits() Returns the current number of available permits.
int	drainPermits() Acquires and returns all permits that are immediately available.
void	reducePermits(int permits) Shrinks the number of available permits by the indicated reduction.
void	release() Releases a permit, returning it to the semaphore.
void	release(int permits) Releases the given number of permits, returning them to the semaphore.
boolean	tryAcquire() Acquires a permit only if one is available at the time of invocation.
boolean	tryAcquire(int permits) Acquires the given number of permits only if all are available at the time of invocation.
boolean	tryAcquire(int permits, long waitTime, TimeUnit unit) Acquires the given number of permits only if all are available within the given waiting time and the current thread has not been interrupted.
boolean	tryAcquire(long waitTime, TimeUnit unit) Acquires a permit from this semaphore, if one becomes available within the given waiting time and the current thread has not been interrupted.
boolean	trySetPermits(int permits) Sets number of permits.

Methods inherited from interface org.redisson.api.RExpirable

clearExpire, expire, expireAt, expireAt, remainTimeToLive

Methods inherited from interface org.redisson.api.RObject

delete, getCodec, getName, isExists, migrate, move, rename, renamenx, touch, unlink

Methods inherited from interface org.redisson.api.RSemaphoreAsync

acquireAsync, acquireAsync, reducePermitsAsync, releaseAsync, releaseAsync, tryAcquireAsync, tryAcquireAsync, tryAcquireAsync, tryAcquireAsync, trySetPermitsAsync

Methods inherited from interface org.redisson.api.RExpirableAsync

clearExpireAsync, expireAsync, expireAtAsync, expireAtAsync, remainTimeToLiveAsync

Methods inherited from interface org.redisson.api.RObjectAsync

deleteAsync, isExistsAsync, migrateAsync, moveAsync, renameAsync, renamenxAsync, touchAsync, unlinkAsync

Method Detail

acquire

void acquire()
      throws InterruptedException

Acquires a permit from this semaphore, blocking until one is available, or the thread is interrupted.

Acquires a permit, if one is available and returns immediately, reducing the number of available permits by one.

If no permit is available then the current thread becomes disabled for thread scheduling purposes and lies dormant until one of two things happens:

• Some other thread invokes the release() method for this semaphore and the current thread is next to be assigned a permit; or
• Some other thread interrupts the current thread.

Throws:

InterruptedException - if the current thread is interrupted

acquire

void acquire(int permits)
      throws InterruptedException

Acquires the given number of permits from this semaphore, blocking until all are available, or the thread is interrupted.

Acquires the given number of permits, if they are available, and returns immediately, reducing the number of available permits by the given amount.

If insufficient permits are available then the current thread becomes disabled for thread scheduling purposes and lies dormant until one of two things happens:

• Some other thread invokes one of the release methods for this semaphore, the current thread is next to be assigned permits and the number of available permits satisfies this request; or
• Some other thread interrupts the current thread.

Parameters:

permits - the number of permits to acquire

Throws:

InterruptedException - if the current thread is interrupted

IllegalArgumentException - if permits is negative

tryAcquire

boolean tryAcquire()

Acquires a permit only if one is available at the time of invocation.

Acquires a permit, if one is available and returns immediately, with the value true, reducing the number of available permits by one.

If no permit is available then this method will return immediately with the value false.

Returns:

true if a permit was acquired and false otherwise

tryAcquire

boolean tryAcquire(int permits)

Acquires the given number of permits only if all are available at the time of invocation.

Acquires a permits, if all are available and returns immediately, with the value true, reducing the number of available permits by given number of permitss.

If no permits are available then this method will return immediately with the value false.

Parameters:

permits - the number of permits to acquire

Returns:

true if a permit was acquired and false otherwise

tryAcquire

boolean tryAcquire(long waitTime,
                   TimeUnit unit)
            throws InterruptedException

Acquires a permit from this semaphore, if one becomes available within the given waiting time and the current thread has not been interrupted.

Acquires a permit, if one is available and returns immediately, with the value true, reducing the number of available permits by one.

If no permit is available then the current thread becomes disabled for thread scheduling purposes and lies dormant until one of three things happens:

• Some other thread invokes the release() method for this semaphore and the current thread is next to be assigned a permit; or
• Some other thread interrupts the current thread; or
• The specified waiting time elapses.

If a permit is acquired then the value true is returned.

If the specified waiting time elapses then the value false is returned. If the time is less than or equal to zero, the method will not wait at all.

Parameters:

waitTime - the maximum time to wait for a permit

unit - the time unit of the timeout argument

Returns:

true if a permit was acquired and false if the waiting time elapsed before a permit was acquired

Throws:

InterruptedException - if the current thread is interrupted

tryAcquire

boolean tryAcquire(int permits,
                   long waitTime,
                   TimeUnit unit)
            throws InterruptedException

Acquires the given number of permits only if all are available within the given waiting time and the current thread has not been interrupted.

Acquires a permits, if all are available and returns immediately, with the value true, reducing the number of available permits by one.

If no permit is available then the current thread becomes disabled for thread scheduling purposes and lies dormant until one of three things happens:

• Some other thread invokes the release() method for this semaphore and the current thread is next to be assigned a permit; or
• Some other thread interrupts the current thread; or
• The specified waiting time elapses.

If a permits is acquired then the value true is returned.

If the specified waiting time elapses then the value false is returned. If the time is less than or equal to zero, the method will not wait at all.

Parameters:

permits - amount

waitTime - the maximum time to wait for a permit

unit - the time unit of the timeout argument

Returns:

true if a permit was acquired and false if the waiting time elapsed before a permit was acquired

Throws:

InterruptedException - if the current thread is interrupted

release

void release()

Releases a permit, returning it to the semaphore.

Releases a permit, increasing the number of available permits by one. If any threads of Redisson client are trying to acquire a permit, then one is selected and given the permit that was just released.

There is no requirement that a thread that releases a permit must have acquired that permit by calling acquire(). Correct usage of a semaphore is established by programming convention in the application.

release

void release(int permits)

Releases the given number of permits, returning them to the semaphore.

Releases the given number of permits, increasing the number of available permits by the given number of permits. If any threads of Redisson client are trying to acquire a permits, then next threads is selected and tries to acquire the permits that was just released.

There is no requirement that a thread that releases a permits must have acquired that permit by calling acquire(). Correct usage of a semaphore is established by programming convention in the application.

Parameters:

permits - amount

availablePermits

int availablePermits()

Returns the current number of available permits.

Returns:

number of available permits

drainPermits

int drainPermits()

Acquires and returns all permits that are immediately available.

Returns:

the number of permits acquired

trySetPermits

boolean trySetPermits(int permits)

Sets number of permits.

Parameters:

permits - - number of permits

Returns:

true if permits has been set successfully, otherwise false.

reducePermits

void reducePermits(int permits)

Shrinks the number of available permits by the indicated reduction.

Parameters:

permits - - reduction the number of permits to remove

Throws:

IllegalArgumentException - if reduction is negative