bionic (3) ualarm.3.gz

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  4.15  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/.

                                                   2017-09-15                                          UALARM(3)