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

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().