#include <time.h>

       int clock_nanosleep(clockid_t clock_id, int flags,
                           const struct timespec *request,
                           struct timespec *remain);

       Link with -lrt.

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

           _XOPEN_SOURCE >= 600 || _POSIX_C_SOURCE >= 200112L

       Like nanosleep(2), clock_nanosleep() allows the calling thread to sleep
       for an interval specified with nanosecond  precision.   It  differs  in
       allowing  the caller to select the clock against which the sleep inter-
       val is to be measured, and in allowing the sleep interval to be  speci-
       fied as either an absolute or a relative value.

       The time values passed to and returned by this call are specified using
       timespec structures, defined as follows:

           struct timespec {
               time_t tv_sec;        /* seconds */
               long   tv_nsec;       /* nanoseconds [0 .. 999999999] */

       The clock_id argument specifies  the  clock  against  which  the  sleep
       interval  is to be measured.  This argument can have one of the follow-
       ing values:

       CLOCK_REALTIME   A settable system-wide real-time clock.

       CLOCK_MONOTONIC  A nonsettable,  monotonically  increasing  clock  that
                        measures time since some unspecified point in the past
                        that does not change after system startup.

                        A settable per-process clock that  measures  CPU  time
                        consumed by all threads in the process.

       See clock_getres(2) for further details on these clocks.

       If flags is 0, then the value specified in request is interpreted as an
       interval relative to the  current  value  of  the  clock  specified  by

       If  flags  is TIMER_ABSTIME, then request is interpreted as an absolute
       time as measured by the clock, clock_id.  If request is  less  than  or
       equal to the current value of the clock, then clock_nanosleep() returns
       immediately without suspending the calling thread.

       On  successfully sleeping for the requested interval, clock_nanosleep()
       returns 0.  If the call is interrupted by a signal handler  or  encoun-
       ters  an error, then it returns one of the positive error number listed
       in ERRORS.

       EFAULT request or remain specified an invalid address.

       EINTR  The sleep was interrupted by a signal handler.

       EINVAL The value in the tv_nsec  field  was  not  in  the  range  0  to
              999999999 or tv_sec was negative.

       EINVAL clock_id was invalid.  (CLOCK_THREAD_CPUTIME_ID is not a permit-
              ted value for clock_id.)

       The clock_nanosleep() system call first appeared in Linux 2.6.  Support
       is available in glibc since version 2.1.


       If  the  interval  specified in request is not an exact multiple of the
       granularity underlying clock (see time(7)), then the interval  will  be
       rounded  up  to  the  next multiple.  Furthermore, after the sleep com-
       pletes, there may still be a delay before the CPU becomes free to  once
       again execute the calling thread.

       Using  an  absolute timer is useful for preventing timer drift problems
       of the type described in nanosleep(2).  (Such problems are  exacerbated
       in  programs  that  try  to restart a relative sleep that is repeatedly
       interrupted by signals.)  To perform a relative sleep that avoids these
       problems,  call clock_gettime(2) for the desired clock, add the desired
       interval to the returned time value, and  then  call  clock_nanosleep()
       with the TIMER_ABSTIME flag.

       clock_nanosleep()  is never restarted after being interrupted by a sig-
       nal handler, regardless of the use  of  the  sigaction(2)  SA_SIGACTION

       The   remain  argument  is  unused,  and  unnecessary,  when  flags  is
       TIMER_ABSTIME.  (An absolute sleep can  be  restarted  using  the  same
       request argument.)

       POSIX.1  specifies that clock_nanosleep() has no effect on signals dis-
       positions or the signal mask.

       POSIX.1 specifies that after changing the value of  the  CLOCK_REALTIME
       clock via clock_settime(2), the new clock value shall be used to deter-
       mine  the  time  at   which   a   thread   blocked   on   an   absolute
       clock_nanosleep()  will  wake up; if the new clock value falls past the
       This page is part of release 3.35 of the Linux  man-pages  project.   A
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       be found at

Linux                             2010-12-03                CLOCK_NANOSLEEP(2)
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