sem_waitsem_trywait
- decrement (lock) a semaphore
LIBRARY
Lb libc
SYNOPSIS
#include <semaphore.h> int
sem_wait (sem_t *sem); int
sem_trywait (sem_t *sem);
DESCRIPTION
The
sem_wait ();
function decrements (locks) the semaphore pointed to by
Fa sem ,
but blocks if the value of
Fa 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
Fa sem
only if the value is non-zero.
Otherwise, the semaphore is not decremented and
an error is returned.
RETURN VALUES
Rv -std
ERRORS
The
sem_wait ();
and
sem_trywait ();
functions will fail if:
Bq Er EINVAL
The
Fa sem
argument
points to an invalid semaphore.
Additionally,
sem_trywait ();
will fail if:
Bq Er EAGAIN
The semaphore value was zero, and thus could not be decremented.
