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

DESCRIPTION
       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.

       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 sus-
       pending 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.

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 a positive error number.

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 prob-
       lems  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  inter-
       val 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 sigac-
       tion(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 3.25 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                                                      2008-07-09                                         CLOCK_NANOSLEEP(2)