Semaphores

Semaphore is one of the oldest synchronization primitives, invented by Edsger Dijkstra. A semaphore is nothing more than an atomic counter that gets decremented by one whenever acquire() is invoked and incremented by one whenever release() is called. The semaphore can be initialized with an initial count value. If none is specified, the semaphore is initialized with a value of one.

Creating semaphore

# semaphore initialized with a default count of 1
semaphore = Semaphore()

# semaphore initialized with count set to 5
sem_with_count = Semaphore(5)

acquire ( )

If a thread invokes acquire() on a semaphore, the semaphore counter is decremented by one. If the count is greater than 0, then the thread immediately returns from the acquire() call. If the semaphore counter is ...