SEM_WAIT(3) BSD Library Functions Manual SEM_WAIT(3)
NAME
sem_wait, sem_trywait -- decrement (lock) a semaphore
LIBRARY
POSIX Real-time Library (librt, -lrt)
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 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
The sem_wait() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indi-
cate the error.
ERRORS
sem_wait() and sem_trywait() will fail if:
[EINVAL] sem points to an invalid semaphore.
Additionally, sem_trywait() will fail if:
[EAGAIN] The semaphore value was zero, and thus could not be decremented.
SEE ALSO
sem_post(3)
STANDARDS
sem_wait() and sem_trywait() conform to ISO/IEC 9945-1:1996 (``POSIX.1'').
BSD
January 22, 2003 BSD
