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$FreeBSD: stable/11/lib/libc/gen/sem_timedwait.3 318971 2017-05-27 00:30:51Z gjb $
.Dd May 24, 2017 .Dt SEM_TIMEDWAIT 3 .Os .Sh NAME .Nm sem_timedwait , .Nm sem_clockwait_np .Nd "lock a semaphore" .Sh LIBRARY .Lb libpthread .Sh SYNOPSIS n semaphore.h n time.h .Ft int .Fn sem_timedwait "sem_t *sem" "const struct timespec *abs_timeout" .Ft int .Fn sem_clockwait_np "sem_t * restrict sem" "clockid_t clock_id" "int flags" "const struct timespec * rqtp" "struct timespec * rmtp" .Sh DESCRIPTION The .Fn sem_timedwait function locks the semaphore referenced by .Fa sem , as in the .Xr 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 .Xr sem_post 3 function, this wait will be terminated when the specified timeout expires.
p The timeout will expire when the absolute time specified by .Fa abs_timeout passes, as measured by the clock on which timeouts are based (that is, when the value of that clock equals or exceeds .Fa abs_timeout ) , or if the absolute time specified by .Fa abs_timeout has already been passed at the time of the call.
p Note that the timeout is based on the .Dv CLOCK_REALTIME clock.
p The validity of the .Fa abs_timeout is not checked if the semaphore can be locked immediately.
p The .Fn sem_clockwait_np function is a more flexible variant of .Fn sem_timedwait . The .Fa clock_id parameter specifies the reference clock. If the .Fa flags parameter contains .Dv TIMER_ABSTIME , then the requested timeout
q Fa rqtp is an absolute timeout; otherwise, the timeout is relative. If this function fails with .Er EINTR and the timeout is relative, a non-NULL .Fa rmtp will be updated to contain the amount of time remaining in the interval
o the requested time minus the time actually slept
c . An absolute timeout has no effect on .Fa rmtp . A single structure can be used for both .Fa rqtp and .Fa rmtp . .Sh RETURN VALUES These functions return zero if the calling process successfully performed the semaphore lock operation on the semaphore designated by .Fa 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 .Va errno to indicate the error. .Sh ERRORS These functions will fail if: l -tag -width Er t Bq Er EINVAL The .Fa sem argument does not refer to a valid semaphore, or the process or thread would have blocked, and the .Fa abs_timeout parameter specified a nanoseconds field value less than zero or greater than or equal to 1000 million. t Bq Er ETIMEDOUT The semaphore could not be locked before the specified timeout expired. t Bq Er EINTR A signal interrupted this function. .El .Sh SEE ALSO .Xr sem_post 3 , .Xr sem_trywait 3 , .Xr sem_wait 3 .Sh STANDARDS The .Fn sem_timedwait function conforms to .St -p1003.1-2004 . The .Fn sem_clockwait_np function is not specified by any standard; it exists only on .Fx at the time of this writing. .Sh HISTORY The .Fn sem_timedwait function first appeared in .Fx 5.0 . The .Fn sem_clockwait_np function first appeared in .Fx 11.1 .