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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 .