sem_timedwait(3RT) Realtime Library Functions sem_timedwait(3RT)NAME
sem_timedwait, sem_reltimedwait_np - lock a semaphore
SYNOPSIS
cc [ flag... ] file... -lrt [ library... ]
#include <semaphore.h>
#include <time.h>
int sem_timedwait(sem_t *restrict sem, const struct timespec *restrict
abs_timeout);
int sem_reltimedwait_np(sem_t *restrict sem, const struct timespec
*restrict rel_timeout);
DESCRIPTION
The sem_timedwait() function locks the semaphore referenced by sem as
in the sem_wait(3RT) function. However, if the semaphore cannot be
locked without waiting for another process or thread to unlock the sem‐
aphore by performing a sem_post(3RT) function, this wait is terminated
when the specified timeout expires.
The sem_reltimedwait_np() function is identical to the sem_timedwait()
function, except that the timeout is specified as a relative time
interval.
For sem_timedwait(), the timeout expires when the absolute time speci‐
fied by abs_timeout passes, as measured by the CLOCK_REALTIME clock
(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.
For sem_reltimedwait_np(), the timeout expires when the time interval
specified by rel_timeout passes, as measured by the CLOCK_REALTIME
clock, or if the time interval specified by rel_timeout is negative at
the time of the call.
The resolution of the timeout is the resolution of the CLOCK_REALTIME
clock. The timespec data type is defined as a structure in the <time.h>
header.
Under no circumstance does the function fail with a timeout if the sem‐
aphore can be locked immediately. The validity of the abs_timeout need
not be checked if the semaphore can be locked immediately.
RETURN VALUES
The sem_timedwait() and sem_reltimedwait_np() functions return 0 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 be unchanged and the function returns -1 and
sets errno to indicate the error.
ERRORS
The sem_timedwait() and sem_reltimedwait_np() functions will fail if:
EINVAL The sem argument does not refer to a valid semaphore.
EINVAL The process or thread would have blocked, and the time‐
out parameter specified a nanoseconds field value less
than zero or greater than or equal to 1,000 million.
ETIMEDOUT The semaphore could not be locked before the specified
timeout expired.
The sem_timedwait() and sem_reltimedwait_np() functions may fail if:
EDEADLK A deadlock condition was detected.
EINTR A signal interrupted this function.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │See below. │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │MT-Safe │
└─────────────────────────────┴─────────────────────────────┘
The sem_timedwait() is function Standard. The sem_reltimedwait_np()
function is Stable.
SEE ALSOsemctl(2), semget(2), semop(2), time(2), sem_post(3RT), sem_try‐
wait(3RT)sem_wait(3RT), attributes(5), standards(5)SunOS 5.10 30 Jan 2004 sem_timedwait(3RT)
