| SEM_WAIT(3) | Library Functions Manual | SEM_WAIT(3) | 
sem_wait, sem_timedwait,
  sem_trywait —
#include <semaphore.h>
int
  
  sem_wait(sem_t
    *sem);
int
  
  sem_timedwait(sem_t
    *sem, const struct
    timespec * restrict abstime);
int
  
  sem_trywait(sem_t
    *sem);
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 performs the
    same action, but will not wait beyond abstime for the
    value of sem to be non-zero.
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.
sem_wait() function returns 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:
EINVAL]Additionally, sem_trywait() will fail
  if:
EAGAIN]sem_timedwait() will also fail if:
ETIMEDOUT]sem_wait() and sem_trywait()
  conform to ISO/IEC 9945-1:1996
  (“POSIX.1”).
| February 29, 2012 | NetBSD 9.3 |