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SEM_WAIT(3) Library Functions Manual SEM_WAIT(3)

sem_wait, sem_timedwait, sem_trywaitdecrement (lock) a semaphore

#include <semaphore.h>

int
sem_wait(sem_t *sem);

int
sem_timedwait(sem_t *sem, const struct timespec *abstime);

int
sem_trywait(sem_t *sem);

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_timedwait() function decrements (locks) the semaphore pointed to by sem, but blocks if the value of sem is zero, until either the value is non-zero and can be decremented or the system time specified by abstime is reached.

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.

The sem_wait(), sem_timedwait(), and sem_trywait() functions return the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

sem_wait(), sem_timedwait(), and sem_trywait() will fail if:

[]
sem points to an invalid semaphore.

Additionally, sem_wait() and sem_timedwait() will fail if:

[]
The call was interrupted by a signal.

Additionally, sem_timedwait() will fail if:

[]
abstime was NULL or specified a nanosecond value less than zero or greater than 1000 million.
[]
The semaphore value was zero and could not be decremented before abstime was reached.

Additionally, sem_trywait() will fail if:

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

sem_destroy(3), sem_getvalue(3), sem_init(3), sem_open(3), sem_post(3)

sem_wait(), sem_timedwait(), and sem_trywait() conform to IEEE Std 1003.1-2008 (“POSIX.1”).

April 24, 2018 OpenBSD-current