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semaphore.h File Reference

POSIX 1003.1b semaphores for process synchronization. More...

Defines

#define EAGAIN
an error code.

Typedefs

typedef unsigned char sem_t
the semaphore type.

Functions

int sem_wait (sem_t * sem)
wait on a semaphore. More...
int sem_trywait (sem_t * sem)
non-blocking check on a semaphore. More...
int sem_post (sem_t * sem)
increase semaphore count. More...

Detailed Description

POSIX 1003.1b semaphores for process synchronization.

Author(s):: Markus L. Noga <noga@inrialpes.fr>

Function Documentation

int sem_wait (sem_t * sem)

wait on a semaphore.

Parameters:: sem - a valid semaphore

suspends the calling thread until the semaphore has non-zero count. It then atomically decreases the semaphore count.

implemented with wait_event().

int sem_trywait (sem_t * sem)

non-blocking check on a semaphore.

Parameters:: sem - a valid semaphore

a non-blocking variant of sem_wait. If the semaphore has non-zero count, the count is atomically decreased and sem_trywait immediately returns 0. If the semaphore count is zero, sem_trywait immediately returns with error EAGAIN.

this is IRQ handler safe.

int sem_post (sem_t * sem)

increase semaphore count.

Parameters:: sem - a valid semaphore

atomically increases the count of the semaphore. This function never blocks and can safely be used in asynchronous signal handlers.