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SEM_WAIT(3)	       FreeBSD Library Functions Manual		   SEM_WAIT(3)

NAME
     sem_wait, sem_trywait -- decrement	(lock) a semaphore

LIBRARY
     Standard C	Library	(libc, -lc)

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
     Upon successful completion, the value 0 is	returned; otherwise the
     value -1 is returned and the global variable errno	is set to indicate the
     error.

ERRORS
     The sem_wait() and	sem_trywait() functions	will fail if:

     [EINVAL]		The sem	argument points	to an invalid semaphore.

     Additionally, sem_wait() will fail	if:

     [EINTR]		A signal interrupted this function.
     Additionally, sem_trywait() will fail if:

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

SEE ALSO
     sem_getvalue(3), sem_post(3), sem_timedwait(3), sem(4)

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

FreeBSD	11.1			April 16, 2013			  FreeBSD 11.1
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS

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