Open Source Software

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:
           (_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200809L)
               || /* Glibc since 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 2.19: */ _BSD_SOURCE
       Before glibc 2.12:
           _BSD_SOURCE || _XOPEN_SOURCE >= 500

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 previously set, or 0 if no alarm was pending.

ERRORS

   EINTR  Interrupted by a signal; see signal(7).

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

ATTRIBUTES

   For  an  explanation  of  the  terms  used   in   this   section,   see
   attributes(7).

   
   Interface  Attribute      Value   
   
   ualarm()   Thread safety  MT-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 4.09 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
   https://www.kernel.org/doc/man-pages/.

                              2016-03-15                         UALARM(3)



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