|SEM_WAIT(3)||FreeBSD Library Functions Manual||SEM_WAIT(3)|
NAMEsem_wait, sem_trywait — decrement (lock) a semaphore
LIBRARYStandard C Library (libc, -lc)
SYNOPSIS#include < semaphore.h>
sem_wait( sem_t *sem);
sem_trywait( sem_t *sem);
DESCRIPTIONThe 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 VALUESUpon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
ERRORSThe 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.
STANDARDSThe sem_wait() and sem_trywait() functions conform to ISO/IEC 9945-1:1996 (“POSIX.1”).
|April 16, 2013||FreeBSD|