SEM_TIMEDWAIT(3C) Standard C Library Functions SEM_TIMEDWAIT(3C)

NAME

sem_timedwait, sem_reltimedwait_np - lock a semaphore

SYNOPSIS

#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(3C) function. However, if the semaphore cannot be locked
without waiting for another process or thread to unlock the semaphore by
performing a sem_post(3C) 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 specified
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
semaphore 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 timeout
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(7) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Committed |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+
|Standard | See below. |
+--------------------+-----------------+


For sem_timedwait(), see standards(7).

SEE ALSO

semctl(2), semget(2), semop(2), time(2), sem_post(3C), sem_trywait(3C),
sem_wait(3C), attributes(7), standards(7)


February 5, 2008 SEM_TIMEDWAIT(3C)