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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 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 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  mea-
       sured  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  avail-
       able 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 information about reporting bugs, can be found at http://www.ker-
       nel.org/doc/man-pages/.



Linux                             2008-07-09                CLOCK_NANOSLEEP(2)

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