NAME

sem_timedwait — lock a semaphore

LIBRARY

POSIX Threads Library (libpthread, -lpthread)

SYNOPSIS

#include < semaphore.h>

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

DESCRIPTION

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.

RETURN VALUES

The sem_timedwait() function returns 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.

ERRORS

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 million.

[ ETIMEDOUT]

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

[ EINTR]

A signal interrupted this function.

SEE ALSO

sem_post(3), sem_trywait(3), sem_wait(3), sem(4)

STANDARDS

The sem_timedwait() function conforms to IEEE Std 1003.1-2004 (“POSIX.1”).

HISTORY

The function first appeared in FreeBSD 5.0.