ualarm(3) - Linux manual page (original) (raw)

ualarm(3) Library Functions Manual ualarm(3)

NAME top

   ualarm - schedule signal after given number of microseconds

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#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 top

   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 top

   This function returns the number of microseconds remaining for any
   alarm that was previously set, or 0 if no alarm was pending.

ERRORS top

   **EINTR** Interrupted by a signal; see [signal(7)](../man7/signal.7.html).

   **EINVAL** _usecs_ or _interval_ is not smaller than 1000000.  (On systems
          where that is considered an error.)

ATTRIBUTES top

   For an explanation of the terms used in this section, see
   [attributes(7)](../man7/attributes.7.html).
   ┌──────────────────────────────────────┬───────────────┬─────────┐
   │ **Interface** │ **Attribute** │ **Value** │
   ├──────────────────────────────────────┼───────────────┼─────────┤
   │ **ualarm**()                             │ Thread safety │ MT-Safe │
   └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS top

   None.

HISTORY top

   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 _usecondst_ 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 _usecondst_ explicitly.

   The interaction of this function with other timer functions such
   as [alarm(2)](../man2/alarm.2.html), [sleep(3)](../man3/sleep.3.html), [nanosleep(2)](../man2/nanosleep.2.html), [setitimer(2)](../man2/setitimer.2.html),
   [timer_create(2)](../man2/timer%5Fcreate.2.html), [timer_delete(2)](../man2/timer%5Fdelete.2.html), [timer_getoverrun(2)](../man2/timer%5Fgetoverrun.2.html),
   [timer_gettime(2)](../man2/timer%5Fgettime.2.html), [timer_settime(2)](../man2/timer%5Fsettime.2.html), [usleep(3)](../man3/usleep.3.html) is unspecified.

   This function is obsolete.  Use [setitimer(2)](../man2/setitimer.2.html) or POSIX interval
   timers ([timer_create(2)](../man2/timer%5Fcreate.2.html), etc.)  instead.

SEE ALSO top

   [alarm(2)](../man2/alarm.2.html), [getitimer(2)](../man2/getitimer.2.html), [nanosleep(2)](../man2/nanosleep.2.html), [select(2)](../man2/select.2.html), [setitimer(2)](../man2/setitimer.2.html),
   [usleep(3)](../man3/usleep.3.html), [time(7)](../man7/time.7.html)

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Linux man-pages 6.10 2024-07-23 ualarm(3)

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