NAME
sem_wait,
sem_trywait —
decrement (lock) a semaphore
LIBRARY
library “libc”
SYNOPSIS
#include
<semaphore.h>
int
sem_wait(sem_t
*sem);
int
sem_trywait(sem_t
*sem);
DESCRIPTION
Thesem_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
Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
ERRORS
The sem_wait() and
sem_trywait() functions will fail if:
- [
EINVAL] - The sem argument points to an invalid semaphore.
Additionally, sem_wait() will fail if:
- [
EINTR] - A signal interrupted this function.
Additionally, sem_trywait() will fail
if:
- [
EAGAIN] - The semaphore value was zero, and thus could not be decremented.
SEE ALSO
STANDARDS
The sem_wait() and
sem_trywait() functions conform to
ISO/IEC 9945-1:1996 (“POSIX.1”).