clock_nanosleep(2) — Linux manual page


clock_nanosleep(2)         System Calls Manual        clock_nanosleep(2)

NAME         top

       clock_nanosleep - high-resolution sleep with specifiable clock

LIBRARY         top

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

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

SYNOPSIS         top

       #include <time.h>

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

   Feature Test Macro Requirements for glibc (see

           _POSIX_C_SOURCE >= 200112L

DESCRIPTION         top

       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

       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:

              A settable system-wide real-time clock.

       CLOCK_TAI (since Linux 3.10)
              A system-wide clock derived from wall-clock time but
              ignoring leap seconds.

              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.

              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 request is interpreted
       as an interval relative to the current value of the clock
       specified by clockid.

       If flags is TIMER_ABSTIME, then request is interpreted as an
       absolute time as measured by the clock, clockid.  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         top

       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         top

       EFAULT request or remain specified an invalid address.

       EINTR  The sleep was interrupted by a signal handler; see

       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.)

              The kernel does not support sleeping against this clockid.

STANDARDS         top


HISTORY         top

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

NOTES         top

       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().

SEE ALSO         top

       clock_getres(2), nanosleep(2), restart_syscall(2),
       timer_create(2), sleep(3), timespec(3), usleep(3), time(7)

Linux man-pages (unreleased)     (date)               clock_nanosleep(2)

Pages that refer to this page: nanosleep(2)prctl(2)restart_syscall(2)syscalls(2)clockid_t(3type)timespec(3type)signal(7)time(7)time_namespaces(7)