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.

   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 caller to sleep for an interval specified with nanosecond precision.  It differs in allow-
       ing 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 exacer-
       bated 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

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

COLOPHON

       This  page is part of release 3.27 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								    2010-09-10							CLOCK_NANOSLEEP(2)