Provided by: manpages-posix-dev_2013a-2_all bug

PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult 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

SYNOPSIS

       #include <semaphore.h>
       #include <time.h>

       int sem_timedwait(sem_t *restrict sem,
           const struct timespec *restrict abstime);

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 abstime passes, as measured by the clock  on
       which  timeouts  are  based  (that is, when the value of that clock equals or exceeds abstime), or if the
       absolute time specified by abstime has already been passed at the time of the call.

       The timeout shall be based on the CLOCK_REALTIME clock.  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 abstime 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 process or thread would have blocked, and the abstime 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.

       EINVAL The sem argument does not refer to a valid semaphore.

       The following sections are informative.

EXAMPLES

       The program shown below operates on an unnamed semaphore. The program expects two command-line arguments.
       The first argument specifies a seconds value that is used to set an alarm timer  to  generate  a  SIGALRM
       signal.  This handler performs a sem_post(3) to increment the semaphore that is being waited on in main()
       using sem_timedwait().  The second command-line argument specifies the length of the timeout, in seconds,
       for sem_timedwait().

           #include <unistd.h>
           #include <stdio.h>
           #include <stdlib.h>
           #include <semaphore.h>
           #include <time.h>
           #include <assert.h>
           #include <errno.h>
           #include <signal.h>

           sem_t sem;

           static void
           handler(int sig)
           {
               int sav_errno = errno;
               static const char info_msg[] = "sem_post() from handler\n";
               write(STDOUT_FILENO, info_msg, sizeof info_msg - 1);
               if (sem_post(&sem) == -1) {
                   static const char err_msg[] = "sem_post() failed\n";
                   write(STDERR_FILENO, err_msg, sizeof err_msg - 1);
                   _exit(EXIT_FAILURE);
               }
               errno = sav_errno;
           }

           int
           main(int argc, char *argv[])
           {
               struct sigaction sa;
               struct timespec ts;
               int s;

               if (argc != 3) {
                   fprintf(stderr, "Usage: %s <alarm-secs> <wait-secs>\n",
                       argv[0]);
                   exit(EXIT_FAILURE);
               }

               if (sem_init(&sem, 0, 0) == -1) {
                   perror("sem_init");
                   exit(EXIT_FAILURE);
               }

               /* Establish SIGALRM handler; set alarm timer using argv[1] */

               sa.sa_handler = handler;
               sigemptyset(&sa.sa_mask);
               sa.sa_flags = 0;
               if (sigaction(SIGALRM, &sa, NULL) == -1) {
                   perror("sigaction");
                   exit(EXIT_FAILURE);
               }

               alarm(atoi(argv[1]));

               /* Calculate relative interval as current time plus
                  number of seconds given argv[2] */

               if (clock_gettime(CLOCK_REALTIME, &ts) == -1) {
                   perror("clock_gettime");
                   exit(EXIT_FAILURE);
               }
               ts.tv_sec += atoi(argv[2]);

               printf("main() about to call sem_timedwait()\n");
               while ((s = sem_timedwait(&sem, &ts)) == -1 && errno == EINTR)
                   continue;       /* Restart if interrupted by handler */

               /* Check what happened */

               if (s == -1) {
                   if (errno == ETIMEDOUT)
                       printf("sem_timedwait() timed out\n");
                   else
                       perror("sem_timedwait");
               } else
                   printf("sem_timedwait() succeeded\n");

               exit((s == 0) ? EXIT_SUCCESS : EXIT_FAILURE);
           }

APPLICATION USAGE

       Applications  using  these  functions  may  be  subject  to  priority inversion, as discussed in the Base
       Definitions volume of POSIX.1‐2008, Section 3.287, Priority Inversion.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       sem_post(), sem_trywait(), semctl(), semget(), semop(), time()

       The Base Definitions volume of POSIX.1‐2008, Section 3.287, Priority Inversion, <semaphore.h>, <time.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers,  Inc
       and  The  Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have  been  introduced
       during   the   conversion  of  the  source  files  to  man  page  format.  To  report  such  errors,  see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .