clock_nanosleep

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



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():
           _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.  In addition,
       the CPU clock IDs returned by clock_getcpuclockid(3) and
       pthread_getcpuclockid(3) can also be passed in clock_id.

       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; 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 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, POSIX.1-2008.

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().

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

COLOPHON
       This page is part of release 5.03 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
       https://www.kernel.org/doc/man-pages/.



Linux                             2017-09-15                CLOCK_NANOSLEEP(2)