This class defines a thread synchonisation object.
Run Time Type functions
Comparison functions
I/O functions
Miscellaneous functions
This class defines a thread synchonisation object. This is in the form of a integer semaphore. The semaphore has a count and a maximum value. The various combinations of count and usage of the Wait() and Signal() functions determine the type of synchronisation mechanism to be employed.The Wait() operation is that if the semaphore count is > 0, decrement the semaphore and return. If it is = 0 then wait (block).
The Signal() operation is that if there are waiting threads then unblock the first one that was blocked. If no waiting threads and the count is less than the maximum then increment the semaphore.
The most common is to create a mutual exclusion zone. A mutex is where a piece of code or data cannot be accessed by more than one thread at a time. To prevent this the PSemaphore is used in the following manner:
PSemaphore mutex(1, 1); // Maximum value of 1 and initial value of 1. ... mutex.Wait(); ... critical section - only one thread at a time here. mutex.Signal(); ...The first thread will pass through the Wait() function, a second thread will block on that function until the first calls the Signal() function, releasing the second thread.
~PSemaphore()
virtual BOOL Wait( const PTimeInterval & timeout )
virtual void Signal()
virtual BOOL WillBlock() const
Alphabetic index HTML hierarchy of classes or Java