UALARM(3)                  Linux Programmer's Manual                 UALARM(3)

       ualarm - schedule signal after given number of microseconds

       #include <unistd.h>

       useconds_t ualarm(useconds_t usecs, useconds_t interval);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

           Since glibc 2.12:
               _BSD_SOURCE ||
                   (_XOPEN_SOURCE >= 500 ||
                       _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) &&
                   !(_POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 700)
           Before glibc 2.12:
               _BSD_SOURCE || _XOPEN_SOURCE >= 500 ||

       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

       If the interval argument is nonzero, further SIGALRM  signals  will  be
       sent every interval microseconds after the first.

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

       EINTR  Interrupted by a signal.

       EINVAL usecs or interval is not  smaller  than  1000000.   (On  systems
              where that is considered an error.)

       For   an   explanation   of   the  terms  used  in  this  section,  see

       |Interface | Attribute     | Value   |
       |ualarm()  | Thread safety | MT-Safe |
       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.

       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_set-
       time(2), usleep(3) is unspecified.

       This  function  is obsolete.  Use setitimer(2) or POSIX interval timers
       (timer_create(2), etc.)  instead.

       alarm(2),   getitimer(2),   nanosleep(2),   select(2),    setitimer(2),
       usleep(3), time(7)

       This  page  is  part of release 4.04 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

                                  2015-03-02                         UALARM(3)
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