UALARM(3)                           Linux Programmer's Manual                           UALARM(3)



NAME
       ualarm - schedule signal after given number of microseconds

SYNOPSIS
       #include <unistd.h>

       useconds_t ualarm(useconds_t usecs, useconds_t interval);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       ualarm():
           Since glibc 2.12:
               _BSD_SOURCE ||
                   (_XOPEN_SOURCE >= 500 ||
                       _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) &&
                   !(_POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 700)
           Before glibc 2.12:
               _BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

DESCRIPTION
       The  ualarm()  function causes the signal SIGALRM to be sent to the invoking process after
       (not less than) usecs microseconds.  The delay may be lengthened slightly  by  any  system
       activity or by the time spent processing the call or by the granularity of system timers.

       Unless caught or ignored, the SIGALRM signal will terminate the process.

       If  the  interval argument is nonzero, further SIGALRM signals will be sent every interval
       microseconds after the first.

RETURN VALUE
       This function returns the number of microseconds remaining for any alarm that  was  previ‐
       ously set, or 0 if no alarm was pending.

ERRORS
       EINTR  Interrupted by a signal.

       EINVAL usecs  or  interval is not smaller than 1000000.  (On systems where that is consid‐
              ered an error.)

ATTRIBUTES
   Multithreading (see pthreads(7))
       The ualarm() function is thread-safe.

CONFORMING TO
       4.3BSD, POSIX.1-2001.  POSIX.1-2001 marks ualarm() as obsolete.  POSIX.1-2008 removes  the
       specification of ualarm().  4.3BSD, SUSv2, and POSIX do not define any errors.

NOTES
       POSIX.1-2001  does  not  specify  what  happens if the usecs argument is 0.  On Linux (and
       probably most other systems), the effect is to cancel any pending alarm.

       The type useconds_t is an unsigned integer type capable of holding integers in  the  range
       [0,1000000].   On  the  original  BSD implementation, and in glibc before version 2.1, the
       arguments to ualarm() were instead typed as unsigned int.  Programs will be more  portable
       if they never mention useconds_t explicitly.

       The  interaction  of  this function with other timer functions such as alarm(2), sleep(3),
       nanosleep(2),   setitimer(2),   timer_create(2),   timer_delete(2),   timer_getoverrun(2),
       timer_gettime(2), timer_settime(2), usleep(3) is unspecified.

       This  function  is  obsolete.  Use setitimer(2) or POSIX interval timers (timer_create(2),
       etc.)  instead.

SEE ALSO
       alarm(2), getitimer(2), nanosleep(2), select(2), setitimer(2), usleep(3), time(7)

COLOPHON
       This page is part of release 3.74 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at http://www.kernel.org/doc/man-pages/.



                                            2013-12-23                                  UALARM(3)