Command Section
SEM_TIMEDWAIT(3)       FreeBSD Library Functions Manual       SEM_TIMEDWAIT(3)

     sem_timedwait, sem_clockwait_np - lock a semaphore

     POSIX Threads Library (libpthread, -lpthread)

     #include <semaphore.h>
     #include <time.h>

     sem_timedwait(sem_t *sem, const struct timespec *abs_timeout);

     sem_clockwait_np(sem_t * restrict sem, clockid_t clock_id, int flags,
         const struct timespec * rqtp, struct timespec * rmtp);

     The sem_timedwait() function locks the semaphore referenced by sem, as in
     the sem_wait(3) function.  However, if the semaphore cannot be locked
     without waiting for another process or thread to unlock the semaphore by
     performing a sem_post(3) function, this wait will be terminated when the
     specified timeout expires.

     The timeout will expire when the absolute time specified by abs_timeout
     passes, as measured by the clock on which timeouts are based (that is,
     when the value of that clock equals or exceeds abs_timeout), or if the
     absolute time specified by abs_timeout has already been passed at the
     time of the call.

     Note that the timeout is based on the CLOCK_REALTIME clock.

     The validity of the abs_timeout is not checked if the semaphore can be
     locked immediately.

     The sem_clockwait_np() function is a more flexible variant of
     sem_timedwait().  The clock_id parameter specifies the reference clock.
     If the flags parameter contains TIMER_ABSTIME, then the requested timeout
     (rqtp) is an absolute timeout; otherwise, the timeout is relative.  If
     this function fails with EINTR and the timeout is relative, a non-NULL
     rmtp will be updated to contain the amount of time remaining in the
     interval (the requested time minus the time actually slept).  An absolute
     timeout has no effect on rmtp.  A single structure can be used for both
     rqtp and rmtp.

     These functions return zero if the calling process successfully performed
     the semaphore lock operation on the semaphore designated by sem.  If the
     call was unsuccessful, the state of the semaphore is unchanged, and the
     function returns a value of -1 and sets the global variable errno to
     indicate the error.

     These functions will fail if:

     [EINVAL]           The sem argument does not refer to a valid semaphore,
                        or the process or thread would have blocked, and the
                        abs_timeout parameter specified a nanoseconds field
                        value less than zero or greater than or equal to 1000

     [ETIMEDOUT]        The semaphore could not be locked before the specified
                        timeout expired.

     [EINTR]            A signal interrupted this function.

     sem_post(3), sem_trywait(3), sem_wait(3)

     The sem_timedwait() function conforms to IEEE Std 1003.1-2004
     (``POSIX.1'').  The sem_clockwait_np() function is not specified by any
     standard; it exists only on FreeBSD at the time of this writing.

     The sem_timedwait() function first appeared in FreeBSD 5.0.  The
     sem_clockwait_np() function first appeared in FreeBSD 11.1.

FreeBSD 11.1-RELEASE-p4          May 24, 2017          FreeBSD 11.1-RELEASE-p4
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