clock_nanosleep(2) — Linux manual page


CLOCK_NANOSLEEP(2)        Linux Programmer's Manual       CLOCK_NANOSLEEP(2)

NAME         top

       clock_nanosleep - high-resolution sleep with specifiable clock

SYNOPSIS         top

       #include <time.h>

       int clock_nanosleep(clockid_t clockid, 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)):

           _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 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 clockid argument specifies the clock against which the sleep
       interval is to be measured.  This argument can have one of the fol‐
       lowing 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_BOOTIME (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 addi‐
       tion, 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

       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 sig‐
       nal 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 signal(7).

       EINVAL The value in the tv_nsec field was not in the range 0 to
              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.

VERSIONS         top

       The clock_nanosleep() system call first appeared in Linux 2.6.
       Support is available in glibc since version 2.1.

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008.

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

       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), usleep(3), time(7)

COLOPHON         top

       This page is part of release 5.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                            2020-04-11               CLOCK_NANOSLEEP(2)

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