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       clock_nanosleep - high-resolution sleep with specifiable clock


       #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)):

       clock_nanosleep(): _XOPEN_SOURCE >= 600


       Like  nanosleep(2), clock_nanosleep() allows the caller to sleep for an
       interval specified with nanosecond precision.  It differs  in  allowing
       the  caller  to select the clock against which the sleep interval is to
       be measured, and in allowing the sleep  interval  to  be  specified  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
       following 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.

       clock_nanosleep() suspends the execution of the  calling  thread  until
       either  at least the time specified by request has elapsed, or a signal
       is delivered that  causes  a  signal  handler  to  be  called  or  that
       terminates the process.

       If  the  call  is  interrupted  by  a signal handler, clock_nanosleep()
       returns -1, and sets errno to EINTR.  In addition,  if  remain  is  not
       NULL, and flags was not TIMER_ABSTIME, it returns the remaining unslept
       time in remain.  This value can then be used to call  clock_nanosleep()
       again and complete a (relative) sleep.


       On  successfully sleeping for the requested interval, clock_nanosleep()
       returns 0.   If  the  call  is  interrupted  by  a  signal  handler  or
       encounters an error, then it returns a positive error number.


       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
              permitted 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
       completes,  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
       signal  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
       dispositions 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
       determine   the   time  at  which  a  thread  blocked  on  an  absolute
       clock_nanosleep() will wake up; if the new clock value falls  past  the
       end  of the sleep interval, then the clock_nanosleep() call will return

       POSIX.1 specifies that changing the value of the  CLOCK_REALTIME  clock
       via  clock_settime(2)  shall have no effect on a thread that is blocked
       on a relative clock_nanosleep().


       nanosleep(2), timer_create(2),  clock_getres(2),  sleep(3),  usleep(3),


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