SEM_TIMEDWAIT(3P)                                   POSIX Programmer's Manual                                  SEM_TIMEDWAIT(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

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 time-
       outs 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 time-
       out  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 implementa-
       tions.

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,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                             SEM_TIMEDWAIT(3P)