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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():
         _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 inter-
     val is to be measured, and in allowing the sleep interval to be  speci-
     fied 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 follow-
     ing 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.  In addition,
     the   CPU   clock   IDs   returned   by   clock_getcpuclockid(3)    and
     pthread_getcpuclockid(3) can also be passed in clock_id.

     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  termi-
     nates 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  com-
     plete 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  encoun-
     ters  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; see signal(7).

     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 permit-
            ted 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, POSIX.1-2008.

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 com-
     pletes, 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 sig-
     nal handler, regardless 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 dis-
     positions 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 deter-
     mine  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().