ualarm(3)                  Library Functions Manual                  ualarm(3)

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)

Linux man-pages 6.7               2023-10-31                         ualarm(3)