FIM.synchronisation
Class Semaphor

java.lang.Object
  |
  +--FIM.synchronisation.Semaphor

public final class Semaphor

extends Object

A standard semaphor as defined in books on operating systems. Negative values are the number of threads waiting, positive values the number of possible waits without blocking.
Because of a collision with java.lang.Object, the methods are all prefixed with "Sem": SemWait, SemSignal, SemValue.

Version:

1.0, 1.7.2000

Author:

Michael Sonntag

See Also:

Thread

Constructor Summary

Semaphor()
Create a new semaphor with a count of 1.

Semaphor(long init)
Create a new semaphor with the provided count.

Method Summary

void	SemInit(long init) Re-Initializes the semaphor with the value provided.
void	SemSignal() Send a signal to the Semaphor.
long	SemValue() Returns the current value of the semaphor.
void	SemWait() Waits till the Semaphor is available.
void	SemWaitNoInterrupt() Waits till the Semaphor is available. ATTENTION: Will ignore any interrupts (no interrupt possible; swallows the InterruptedException) and wait again till finally a SemSignal is done.

Methods inherited from class java.lang.Object

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

Constructor Detail

Semaphor

public Semaphor()

Create a new semaphor with a count of 1.

Semaphor

public Semaphor(long init)

Create a new semaphor with the provided count.

Parameters:

init - initial value of the semaphor

Method Detail

SemInit

public void SemInit(long init)

Re-Initializes the semaphor with the value provided. Take care, strange results may happen if this change is not expected by all other threads (and they are progammed for this)! If threads are waiting and the parameter is greater than their number, the according number of them is set free immediately. If the parameter is less than the number of waiting threads, the waiting threads are set free with the first SemSignals and the excess value is only required for new SemWaits to not block.

Parameters:

init - the value to initialize the semaphor with

SemValue

public long SemValue()

Returns the current value of the semaphor. Three ranges are possible:

• Positive value: That may SemWait will succeed without blocking
• Zero value: No thread is waiting, the next call to SemWait will block till SemSignal is called
• Negative value: That many threads are currently waiting

Returns:

current value

SemWait

public void SemWait()
             throws InterruptedException

Waits till the Semaphor is available.

Throws:

InterruptedException - if interrupt is called

See Also:

Thread

SemWaitNoInterrupt

public void SemWaitNoInterrupt()

Waits till the Semaphor is available.
ATTENTION: Will ignore any interrupts (no interrupt possible; swallows the InterruptedException) and wait again till finally a SemSignal is done. No termination in between possible!

See Also:

Thread

SemSignal

public void SemSignal()

Send a signal to the Semaphor. If threads are waiting, one of them is started. Which one is NOT defined.