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NAME

       clock_nanosleep - high-resolution sleep with specifiable clock

SYNOPSIS

       #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 || _POSIX_C_SOURCE >= 200112L

DESCRIPTION

       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
       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.

       CLOCK_PROCESS_CPUTIME_ID
                        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
       clock_id.

       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() fails
       with the error 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.

RETURN VALUE

       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 one of the positive error number
       listed in ERRORS.

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
              permitted value for clock_id.)

VERSIONS

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

CONFORMING TO

       POSIX.1-2001.

NOTES

       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
       flag.

       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
       immediately.

       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().

SEE ALSO

       clock_getres(2),  nanosleep(2),  timer_create(2),  sleep(3), usleep(3),
       time(7)

COLOPHON

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