Semaphores

Semaphores were, as mentioned earlier, not part of the original Pthreads extension to the POSIX specification. They are declared in the semaphore.h header for this reason.

In essence, semaphores are simple integers, generally used as a resource count. To make them thread-safe, atomic operations (check and lock) are used. POSIX semaphores support the initializing, destroying, incrementing and decrementing of a semaphore as well as waiting for the semaphore to reach a non-zero value.