Ubuntu Manpage: clock_nanosleep - high-resolution sleep with specifiable clock

name
library
synopsis
description
return value
errors
standards
history
notes
see also

NAME

       clock_nanosleep - high-resolution sleep with specifiable clock

LIBRARY

       Standard C library (libc, -lc), since glibc 2.17

       Before glibc 2.17, Real-time library (librt, -lrt)

SYNOPSIS

       #include <time.h>

       int clock_nanosleep(clockid_t clockid, int flags,
                           const struct timespec *t,
                           struct timespec *_Nullable remain);

   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
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(3) structures.

The clockid 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_TAI (since Linux 3.10)
A system-wide clock derived from wall-clock time but counting leap seconds.

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_BOOTTIME (since Linux 2.6.39)
Identical to CLOCK_MONOTONIC, except that it also includes any time that the system is suspended.

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 clockid.

If flags is 0, then the value specified in t is interpreted as an interval relative to the current value
of the clock specified by clockid.

If flags is TIMER_ABSTIME, then t is interpreted as an absolute time as measured by the clock, clockid.
If t 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 t 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 t 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, 999999999] or tv_sec was negative.

       EINVAL clockid was invalid.  (CLOCK_THREAD_CPUTIME_ID is not a permitted value for clockid.)

       ENOTSUP
              The kernel does not support sleeping against this clockid.

STANDARDS

       POSIX.1-2008.

HISTORY

       POSIX.1-2001.  Linux 2.6, glibc 2.1.

NOTES

       If the interval specified in t 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_RESTART flag.

       The remain argument is unused, and unnecessary, when flags is TIMER_ABSTIME.  (An absolute sleep  can  be
       restarted using the same t 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().