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().