Package com.oracle.coherence.concurrent

Interface Semaphore

All Known Implementing Classes:
LocalSemaphore, RemoteSemaphore
public interface Semaphore
Since:
21.12
Author:
Aleks Seovic 2021.12.05

  • 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.
    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 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 Details

    • 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.

      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.
      Throws:
      InterruptedException - 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.

      Even when this semaphore has been set to use a fair ordering policy, a call to tryAcquire() will immediately acquire a permit if one is available, whether or not other threads are currently waiting. This "barging" behavior can be useful in certain circumstances, even though it breaks fairness. If you want to honor the fairness setting, then use tryAcquire(0, TimeUnit.SECONDS) which is almost equivalent (it also detects interruption).

      Returns:
      true if a permit was acquired and false otherwise

    • tryAcquire

      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.

      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 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 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.

    • 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. 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().
      Parameters:
      permits - the number of permits to acquire
      Throws:
      InterruptedException - if the current thread is interrupted
      IllegalArgumentException - if permits is negative

    • 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. 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.

      Parameters:
      permits - the number of permits to acquire
      Throws:
      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.

      Even when this semaphore has been set to use a fair ordering policy, a call to tryAcquire will immediately acquire a permit if one is available, whether or not other threads are currently waiting. This "barging" behavior can be useful in certain circumstances, even though it breaks fairness. If you want to honor the fairness 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

    • tryAcquire

      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().

      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 if the waiting time elapsed before all permits were acquired
      Throws:
      InterruptedException - 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 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.

      Parameters:
      permits - the number of permits to release
      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, or if negative permits are available, releases them. Upon return, zero permits are available.
      Returns:
      the number of permits acquired or, if negative, the number released