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 Details

    • 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 Details

    • 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.