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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.

   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 pre-
       cision.  It differs in allowing the caller to select the clock against which the sleep interval is to  be  mea-
       sured, 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 fol-
       lows:

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

COLOPHON
       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-07-09                CLOCK_NANOSLEEP(2)