#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.)

       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.

       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),
       description  of  the project, and information about reporting bugs, can
       be found at

                                  2010-09-20                         UALARM(3)
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