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 <= 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 5.13 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/.

                                            2021-03-22                                  UALARM(3)