NAME

       ualarm - schedule signal after given number of microseconds

LIBRARY

       Standard C library (libc, -lc)

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 >= 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 │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       None.

HISTORY

       4.3BSD, POSIX.1-2001.  POSIX.1-2001 marks it as obsolete.  Removed in POSIX.1-2008.

       4.3BSD, SUSv2, and POSIX do not define any errors.

       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  glibc  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)