Package com.oracle.coherence.concurrent

Class RemoteSemaphore

java.lang.Object

com.oracle.coherence.concurrent.RemoteSemaphore

All Implemented Interfaces:

Semaphore

public class RemoteSemaphore
extends Object
implements Semaphore

A distributed counting semaphore. Conceptually, a semaphore maintains a set of permits. Each acquire() blocks if necessary until a permit is available, and then takes it. Each release() adds a permit, potentially releasing a blocking acquirer. However, no actual permit objects are used; the RemoteSemaphore just keeps a count of the number available and acts accordingly.

Since:

21.12

Author:

Vaso Putica 2021.12.01

Constructor Summary

Constructors

Constructor	Description
RemoteSemaphore(String sName, int permits, NamedMap<String,com.oracle.coherence.concurrent.internal.SemaphoreStatus> semaphores)	Create an instance of RemoteSemaphore

Method Summary

Modifier and Type	Method	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.
int	drainPermits()	Acquires and returns all permits that are immediately available, or if negative permits are available, releases them.
int	getInitialPermits()	Returns number of permits that were used to initialise this semaphore.
boolean	isAcquiredByCurrentThread()	Queries if an permit is acquired by the current thread.
protected void	reducePermits(int reduction)	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.
String	toString()	Returns a string identifying this semaphore, as well as its state.
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.

Methods inherited from class java.lang.Object

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

Constructor Detail

RemoteSemaphore

public RemoteSemaphore(String sName,
                       int permits,
                       NamedMap<String,com.oracle.coherence.concurrent.internal.SemaphoreStatus> semaphores)

Create an instance of RemoteSemaphore

Parameters:

sName - the name of the semaphore

permits - the initial number of permits available

semaphores - the NamedMap that stores this semaphore's state

Method Detail

acquire

public 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.

If the current thread:

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

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

Specified by:

acquire in interface Semaphore

Throws:

InterruptedException - if the current thread is interrupted

acquireUninterruptibly

public 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.

Specified by:

acquireUninterruptibly in interface Semaphore

tryAcquire

public 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.

Specified by:

tryAcquire in interface Semaphore

Returns:

true if a permit was acquired and false otherwise

tryAcquire

public boolean tryAcquire(long timeout,
                          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 current thread:

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

then InterruptedException 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.

Specified by:

tryAcquire in interface Semaphore

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:

InterruptedException - if the current thread is interrupted

release

public 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.

Specified by:

release in interface Semaphore

acquire

public 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. This method has the same effect as the loop for (int i = 0; i < permits; ++i) acquire(); except that it atomically acquires the permits all at once:

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 and 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 InterruptedException 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().

Specified by:

acquire in interface Semaphore

Parameters:

permits - the number of permits to acquire

Throws:

InterruptedException - if the current thread is interrupted

IllegalArgumentException - if permits is negative

acquireUninterruptibly

public 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. This method has the same effect as the loop for (int i = 0; i < permits; ++i) acquireUninterruptibly(); except that it atomically acquires the permits all at once:

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 and 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.

Specified by:

acquireUninterruptibly in interface Semaphore

Parameters:

permits - the number of permits to acquire

Throws:

IllegalArgumentException - if permits is negative

tryAcquire

public 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.

Specified by:

tryAcquire in interface Semaphore

Parameters:

permits - the number of permits to acquire

Returns:

true if the permits were acquired and false otherwise

Throws:

IllegalArgumentException - if permits is negative

tryAcquire

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

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 and 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 InterruptedException 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().

Specified by:

tryAcquire in interface Semaphore

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:

InterruptedException - if the current thread is interrupted

IllegalArgumentException - if permits is negative

release

public 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 thread 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.

Specified by:

release in interface Semaphore

Parameters:

permits - the number of permits to release

Throws:

IllegalArgumentException - if permits is negative

availablePermits

public int availablePermits()

Returns the current number of permits available in this semaphore.

This method is typically used for debugging and testing purposes.

Specified by:

availablePermits in interface Semaphore

Returns:

the number of permits available in this semaphore

drainPermits

public int drainPermits()

Acquires and returns all permits that are immediately available, or if negative permits are available, releases them. Upon return, zero permits are available.

Specified by:

drainPermits in interface Semaphore

Returns:

the number of permits acquired or, if negative, the number released

reducePermits

protected void reducePermits(int reduction)

Shrinks the number of available permits by the indicated reduction. This method can be useful in subclasses that use semaphores to track resources that become unavailable. This method differs from acquire in that it does not block waiting for permits to become available.

Parameters:

reduction - the number of permits to remove

Throws:

IllegalArgumentException - if reduction is negative

isAcquiredByCurrentThread

public boolean isAcquiredByCurrentThread()

Queries if an permit is acquired by the current thread.

Returns:

true if current thread acquired permit and false otherwise

toString

public String toString()

Returns a string identifying this semaphore, as well as its state. The state, in brackets, includes the String "Permits =" followed by the number of permits.

Overrides:

toString in class Object

Returns:

a string identifying this semaphore, as well as its state

getInitialPermits

public int getInitialPermits()

Returns number of permits that were used to initialise this semaphore.

Returns:

initial number of permits that were used to initialise this semaphore.