org.apache.ignite

Interface IgniteSemaphore

All Superinterfaces:

AutoCloseable, Closeable

public interface IgniteSemaphore
extends Closeable

This interface provides a rich API for working with distributed semaphore.

Description

Functionality

Distributed semaphore provides functionality similar to java.util.concurrent.Semaphore.

Creating Distributed Semaphore

Instance of cache semaphore can be created by calling the following method: Ignite.semaphore(String, int, boolean, boolean).

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.
void	acquireUninterruptibly() Acquires a permit from this semaphore, blocking until one is available.
void	acquireUninterruptibly(int permits) Acquires the given number of permits from this semaphore, blocking until all are available.
int	availablePermits() Returns the current number of permits available in this semaphore.
void	close() Removes this semaphore.
int	drainPermits() Acquires and returns all permits that are immediately available.
int	getQueueLength() Returns an estimate of the number of nodes waiting to acquire.
boolean	hasQueuedThreads() Queries whether any threads are waiting to acquire.
boolean	isBroken() Gets broken status of the semaphore.
boolean	isFailoverSafe() Returns true if this semaphore is safe to use after node failure.
String	name() Gets name of the semaphore.
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	removed() Gets removed status of the semaphore.
boolean	tryAcquire() Acquires a permit from this semaphore, only if one is available at the time of invocation.
boolean	tryAcquire(int permits) Acquires the given number of permits from this semaphore, only if all are available at the time of invocation.
boolean	tryAcquire(int permits, long timeout, TimeUnit unit) Acquires the given number of permits from this semaphore, if all become available within the given waiting time and the current thread has not been interrupted.
boolean	tryAcquire(long timeout, 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.

Method Detail

name

String name()

Gets name of the semaphore.

Returns:

Name of the semaphore.

acquire

void acquire()
      throws IgniteInterruptedException

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.

If the current thread:

• has its interrupted status set on entry to this method; or
• is interrupted while waiting for a permit,

then IgniteInterruptedException is thrown and the current thread's interrupted status is cleared.

Throws:

IgniteInterruptedException - if the current thread is interrupted

acquireUninterruptibly

void acquireUninterruptibly()

Acquires a permit from this semaphore, blocking until one is available.

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 some other thread invokes the release() method for this semaphore and the current thread is next to be assigned a permit.

If the current thread is interrupted while waiting for a permit then it will continue to wait, but the time at which the thread is assigned a permit may change compared to the time it would have received the permit had no interruption occurred. When the thread does return from this method its interrupt status will be set.

tryAcquire

boolean tryAcquire()

Acquires a permit from this semaphore, 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(long timeout,
                   TimeUnit unit)
            throws IgniteInterruptedException

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 current thread:

• has its interrupted status set on entry to this method; or
• is interrupted while waiting to acquire a permit,

then IgniteInterruptedException is thrown and the current thread's interrupted status is cleared.

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:

timeout - 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:

IgniteInterruptedException - if the current thread is interrupted

acquireUninterruptibly

void acquireUninterruptibly(int permits)

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

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 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.

If the current thread is interrupted while waiting for permits then it will continue to wait and its position in the queue is not affected. When the thread does return from this method its interrupt status will be set.

Parameters:

permits - the number of permits to acquire

Throws:

IllegalArgumentException - if permits is negative

availablePermits

int availablePermits()

Returns the current number of permits available in this semaphore.

This method is typically used for debugging and testing purposes.

Returns:

the number of permits available in this semaphore

drainPermits

int drainPermits()

Acquires and returns all permits that are immediately available.

Returns:

the number of permits acquired

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 are trying to acquire a permit, then one is selected and given the permit that was just released. That thread is (re)enabled for thread scheduling purposes.

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.

tryAcquire

boolean tryAcquire(int permits,
                   long timeout,
                   TimeUnit unit)
            throws IgniteInterruptedException

Acquires the given number of permits from this semaphore, if all become available within the given waiting time and the current thread has not been interrupted.

Acquires the given number of permits, if they are available and returns immediately, with the value true, 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 three 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; or
• The specified waiting time elapses.

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

If the current thread:

• has its interrupted status set on entry to this method; or
• is interrupted while waiting to acquire the permits,

then IgniteInterruptedException is thrown and the current thread's interrupted status is cleared. Any permits that were to be assigned to this thread, are instead assigned to other threads trying to acquire permits, as if the permits had been made available by a call to release().

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. Any permits that were to be assigned to this thread, are instead assigned to other threads trying to acquire permits, as if the permits had been made available by a call to release().

Parameters:

permits - the number of permits to acquire

timeout - the maximum time to wait for the permits

unit - the time unit of the timeout argument

Returns:

true if all permits were acquired and false if the waiting time elapsed before all permits were acquired

Throws:

IgniteInterruptedException - if the current thread is interrupted

IllegalArgumentException - if permits is negative

tryAcquire

boolean tryAcquire(int permits)

Acquires the given number of permits from this semaphore, only if all are available at the time of invocation.

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

If insufficient permits are available then this method will return immediately with the value false and the number of available permits is unchanged.

If you want to honor the failoverSafe setting, then use tryAcquire(permits, 0, TimeUnit.SECONDS) which is almost equivalent (it also detects interruption).

Parameters:

permits - the number of permits to acquire

Returns:

true if the permits were acquired and false otherwise

Throws:

IllegalArgumentException - if permits is negative

acquire

void acquire(int permits)
      throws IgniteInterruptedException

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.

If the current thread:

• has its interrupted status set on entry to this method; or
• is interrupted while waiting for a permit,

then IgniteInterruptedException is thrown and the current thread's interrupted status is cleared. Any permits that were to be assigned to this thread are instead assigned to other threads trying to acquire permits, as if permits had been made available by a call to release().

Parameters:

permits - the number of permits to acquire

Throws:

IgniteInterruptedException - if the current thread is interrupted

IllegalArgumentException - if permits is negative

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 that amount. If any threads are trying to acquire permits, then one is selected and given the permits that were just released. If the number of available permits satisfies that thread's request then that thread is (re)enabled for thread scheduling purposes; otherwise the thread will wait until sufficient permits are available. If there are still permits available after this thread's request has been satisfied, then those permits are assigned in turn to other threads trying to acquire permits.

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.

Parameters:

permits - the number of permits to release

Throws:

IllegalArgumentException - if permits is negative

isFailoverSafe

boolean isFailoverSafe()

Returns true if this semaphore is safe to use after node failure. If not, IgniteInterruptedException is thrown on every other node after node failure.

Returns:

true if this semaphore has failoverSafe set true

hasQueuedThreads

boolean hasQueuedThreads()

Queries whether any threads are waiting to acquire. Note that because cancellations may occur at any time, a true return does not guarantee that any other thread will ever acquire. This method is designed primarily for use in monitoring of the system state.

Returns:

true if there may be other threads waiting to acquire the lock

getQueueLength

int getQueueLength()

Returns an estimate of the number of nodes waiting to acquire. The value is only an estimate because the number of nodes that are waiting may change dynamically while this method traverses internal data structures. This method is designed for use in monitoring of the system state, not for synchronization control.

Returns:

the estimated number of nodes waiting for this lock

isBroken

boolean isBroken()

Gets broken status of the semaphore.

Returns:

True if a node failed on this semaphore and failoverSafe flag was set to false, false otherwise.

removed

boolean removed()

Gets removed status of the semaphore.

Returns:

True if semaphore was removed from cache, false otherwise.

close

void close()

Removes this semaphore.

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Throws:

IgniteException - If operation failed.