xenial (2) clock_nanosleep.2.gz

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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.  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.

       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

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