SEM_TIMEDWAIT(3) BSD Library Functions Manual SEM_TIMEDWAIT(3)NAMEsem_timedwait — lock a semaphore
POSIX Threads Library (libpthread, -lpthread)
sem_timedwait(sem_t *sem, const struct timespec *abs_timeout);
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
The sem_timedwait() function returns zero if the calling process success‐
fully 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.
The sem_timedwait() function 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
[EINTR] A signal interrupted this function.
SEE ALSOsem_post(3), sem_trywait(3), sem_wait(3), sem(4)STANDARDS
The sem_timedwait() function conforms to IEEE Std 1003.1-2004
The function first appeared in FreeBSD 5.0.
BSD March 3, 2008 BSD