NAME

sem_wait, sem_trywait - decrement (lock) a semaphore

LIBRARY

POSIX Real-time Library (librt, -lrt)

SYNOPSIS



int sem_wait(sem_t *sem)

int sem_trywait(sem_t *sem)

DESCRIPTION

The sem_wait() function decrements (locks) the semaphore pointed to by sem, but blocks if the value of sem is zero, until the value is non-zero and the value can be decremented.

The sem_trywait() function decrements (locks) the semaphore pointed to by sem only if the value is non-zero. Otherwise, the semaphore is not decremented and an error is returned.

RETURN VALUES

ERRORS

sem_wait() and sem_trywait() will fail if:

[EINVAL]
sem points to an invalid semaphore.

Additionally, sem_trywait() will fail if:

[EAGAIN]
The semaphore value was zero, and thus could not be decremented.

SEE ALSO

sem_post(3)

STANDARDS

sem_wait() and sem_trywait() conform to ISO/IEC 9945-1:1996 (``POSIX.1'') .