SEM_TIMEDWAIT(P) POSIX Programmer's Manual SEM_TIMEDWAIT(P)
sem_timedwait - lock a semaphore (ADVANCED REALTIME)
int sem_timedwait(sem_t *restrict sem,
const struct timespec *restrict abs_timeout);
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 mea-
sured 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
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.
The sem_timedwait() function shall return zero if the calling process successfully per-
formed 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.
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.
The semaphore could not be locked before the specified timeout expired.
The sem_timedwait() function may fail if:
A deadlock condition was detected.
EINTR A signal interrupted this function.
The following sections are informative.
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.
sem_post() , sem_trywait() , sem_wait() , semctl() , semget() , semop() , time() , the
Base Definitions volume of IEEE Std 1003.1-2001, <semaphore.h>, <time.h>
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 SEM_TIMEDWAIT(P)