trusty (3) sem_timedwait.3posix.gz

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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>


       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 .