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

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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():
           _XOPEN_SOURCE >= 600 || _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 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 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.

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
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 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  available  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_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 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().

COLOPHON

       This page is part of release 3.54 of the Linux man-pages project.  A  description  of  the  project,  and
       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

Linux                                              2013-07-30                                 CLOCK_NANOSLEEP(2)