MirBSD manpage: sem_trywait(3), sem_wait(3)

SEM_WAIT(3)                BSD Programmer's Manual                 SEM_WAIT(3)

NAME

     sem_wait, sem_trywait - decrement (lock) a semaphore

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 decre-
     mented 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 indicate 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 decre-
                   mented.

SEE ALSO

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

STANDARDS

     sem_wait() and sem_trywait() conform to ISO/IEC 9945-1:1996 ("POSIX.1").

MirBSD #10-current            February 15, 2000                              1