ISemaphore (Hazelcast Root 3.11 API)

All Superinterfaces:

DistributedObject

All Known Implementing Classes:

ClientSemaphoreProxy, SemaphoreProxy
```
public interface ISemaphore
extends DistributedObject
```
ISemaphore is a backed-up distributed alternative to the Semaphore.
ISemaphore is a cluster-wide counting semaphore. Conceptually, it 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 semaphore just keeps a count of the number available and acts accordingly.
The Hazelcast distributed semaphore implementation guarantees that threads invoking any of the acquire methods are selected to obtain permits in the order in which their invocation of those methods was processed(first-in-first-out; FIFO). Note that FIFO ordering necessarily applies to specific internal points of execution within the cluster. Therefore, it is possible for one member to invoke acquire before another, but reach the ordering point after the other, and similarly upon return from the method.
This class also provides convenience methods to acquire and release multiple permits at a time. Beware of the increased risk of indefinite postponement when using the multiple acquire. If a single permit is released to a semaphore that is currently blocking, a thread waiting for one permit will acquire it before a thread waiting for multiple permits regardless of the call order.
Correct usage of a semaphore is established by programming convention in the application.
During a split-brain scenario, atomicity is lost. The same ISemaphore can exist within each cluster partition and therefore the permit counters within will diverge. When the cluster heals, Hazelcast will choose one of the ISemaphores, by default this is selected from the largest partitioned cluster (by number of members). If the cluster sizes are all equal then a random ISemaphore will be chosen. Supports Quorum QuorumConfig since 3.10 in cluster versions 3.10 and higher.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method and Description
`void`	`acquire()` Acquires a permit if one is available, and returns immediately, reducing the number of available permits by one.
`void`	`acquire(int permits)` Acquires the given number of permits if they are available, and returns immediately, reducing the number of available permits by the given amount.
`int`	`availablePermits()` Returns the current number of permits currently available in this semaphore.
`int`	`drainPermits()` Acquires and returns all permits that are immediately available.
`String`	`getName()` Returns the name of this ISemaphore instance.
`void`	`increasePermits(int increase)` Increases the number of available permits by the indicated amount.
`boolean`	`init(int permits)` Try to initialize this ISemaphore instance with the given permit count
`void`	`reducePermits(int reduction)` Shrinks the number of available permits by the indicated reduction.
`void`	`release()` Releases a permit, increasing the number of available permits by one.
`void`	`release(int permits)` Releases the given number of permits, increasing the number of available permits by that amount.
`boolean`	`tryAcquire()` Acquires a permit, if one is available and returns immediately, with the value `true`, reducing the number of available permits by one.
`boolean`	`tryAcquire(int permits)` 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.
`boolean`	`tryAcquire(int permits, long timeout, TimeUnit unit)` 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.
`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 interface com.hazelcast.core.DistributedObject
destroy, getPartitionKey, getServiceName

- Method Detail
  - getName
```
String getName()
```
    Returns the name of this ISemaphore instance.
    
    Specified by:
    
    getName in interface DistributedObject
    
    Returns:
    
    name of this instance
  - init
```
boolean init(int permits)
```
    Try to initialize this ISemaphore instance with the given permit count
    
    Parameters:
    
    permits - the given permit count
    
    Returns:
    
    true if initialization success
  - acquire
```
void acquire()
      throws InterruptedException
```
    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 three things happens:
    - some other thread invokes one of the release() methods for this semaphore and the current thread is next to be assigned a permit,
    - this ISemaphore instance is destroyed, 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
    
    IllegalStateException - if hazelcast instance is shutdown while waiting
  - acquire
```
void acquire(int permits)
      throws InterruptedException
```
    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 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,
    - this ISemaphore instance is destroyed, 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.
    Parameters:
    
    permits - the number of permits to acquire
    
    Throws:
    
    InterruptedException - if the current thread is interrupted
    
    IllegalArgumentException - if permits is negative
    
    IllegalStateException - if hazelcast instance is shutdown while waiting
  - availablePermits
```
int availablePermits()
```
    Returns the current number of permits currently 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 drained
  - reducePermits
```
void reducePermits(int reduction)
```
    Shrinks the number of available permits by the indicated reduction.
    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
  - increasePermits
```
void increasePermits(int increase)
```
    Increases the number of available permits by the indicated amount. This method differs from release in that it does not effect the amount of permits this caller has attached.
    
    Parameters:
    
    increase - the number of permits to add
    
    Throws:
    
    IllegalArgumentException - if increase is negative
  - release
```
void release()
```
    Releases a permit, increasing the number of available permits by one. If any threads in the cluster 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 one of the acquire methods. Correct usage of a semaphore is established by programming convention in the application.
  - release
```
void release(int permits)
```
    Releases the given number of permits, increasing the number of available permits by that amount.
    There is no requirement that a thread that releases a permit must have acquired that permit by calling one of the acquire methods. 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
  - tryAcquire
```
boolean tryAcquire()
```
    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, 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.
    
    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(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 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.
    If the current thread:
    - has its interrupted status set on entry to this method; or
    - is interrupted while waiting
    then InterruptedException is thrown and the current thread's interrupted status is cleared.
    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
    
    IllegalStateException - if hazelcast instance is shutdown while waiting
  - tryAcquire
```
boolean tryAcquire(int permits,
                   long timeout,
                   TimeUnit unit)
            throws InterruptedException
```
    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 true is returned.
    If the specified waiting time elapses then false is returned. If the time is less than or equal to zero, the method will not wait at all.
    If the current thread:
    - has its interrupted status set on entry to this method, or
    - is interrupted while waiting
    then InterruptedException is thrown and the current thread's interrupted status is cleared.
    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, false if the waiting time elapsed before all permits could be acquired
    
    Throws:
    
    InterruptedException - if the current thread is interrupted
    
    IllegalArgumentException - if permits is negative
    
    IllegalStateException - if hazelcast instance is shutdown while waiting

Interface ISemaphore

Method Summary

Methods inherited from interface com.hazelcast.core.DistributedObject

Method Detail

getName

init

acquire

acquire

availablePermits

drainPermits

reducePermits

increasePermits

release

release

tryAcquire

tryAcquire

tryAcquire

tryAcquire