NAME
sem_timedwait - lock a semaphore (ADVANCED REALTIME)
SYNOPSIS
#include <semaphore.h>
#include <time.h>
int sem_timedwait(sem_t *restrict sem,
const struct timespec *restrict abs_timeout);
DESCRIPTION
The sem_timedwait() function shall lock the semaphore referenced by sem
as in the sem_wait() function. However, if the semaphore cannot be
locked without waiting for another process or thread to unlock the
semaphore by performing a sem_post() function, this wait shall be
terminated when the specified timeout expires.
The timeout shall 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.
If the Timers option is supported, the timeout shall be based on the
CLOCK_REALTIME clock. If the Timers option is not supported, the
timeout shall be based on the system clock as returned by the time()
function. The resolution of the timeout shall be the resolution of the
clock on which it is based. The timespec data type is defined as a
structure in the <time.h> header.
Under no circumstance shall 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 VALUE
The sem_timedwait() function shall return 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 shall be unchanged, and the function shall return a value of
-1 and set errno to indicate the error.
ERRORS
The sem_timedwait() function shall fail if:
EINVAL The sem argument does not refer to a valid semaphore.
EINVAL 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.
The sem_timedwait() function may fail if:
EDEADLK
A deadlock condition was detected.
EINTR A signal interrupted this function.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
Applications using these functions may be subject to priority
inversion, as discussed in the Base Definitions volume of
IEEE Std 1003.1-2001, Section 3.285, Priority Inversion.
The sem_timedwait() function is part of the Semaphores and Timeouts
options and need not be provided on all implementations.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
sem_post() , sem_trywait() , sem_wait() , semctl() , semget() , semop()
, time() , the Base Definitions volume of IEEE Std 1003.1-2001,
<semaphore.h>, <time.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .