sem_wait(3) - NetBSD Manual Pages

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SEM_WAIT(3)             NetBSD 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 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
                        decremented.


SEE ALSO

     sem_post(3)


STANDARDS

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

NetBSD 5.0                     January 22, 2003                     NetBSD 5.0