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 .

IEEE/The Open Group                                   2003                                      SEM_TIMEDWAIT(P)