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CLOCK_NANOSLEEP(2)		    Linux Programmer's Manual		       CLOCK_NANOSLEEP(2)

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 (only for glibc versions before 2.17).

   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 inter-
       val 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  struc-
       tures, 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 mea-
       sured.  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 han-
       dler 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  underly-
       ing  clock (see time(7)), then the interval will be rounded up to the next multiple.  Fur-
       thermore, 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,  regard-
       less of the use of the sigaction(2) SA_RESTART 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 sig-
       nal mask.

       POSIX.1 specifies that after changing the value of the CLOCK_REALTIME clock via clock_set-
       time(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),	restart_syscall(2), timer_create(2), sleep(3), usleep(3),
       time(7)

COLOPHON
       This page is part of release 3.53 of the Linux man-pages project.  A  description  of  the
       project,     and    information	  about    reporting	bugs,	 can	be    found    at
       http://www.kernel.org/doc/man-pages/.

Linux					    2013-07-30			       CLOCK_NANOSLEEP(2)
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