huschi.net

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 inter-
       val is to be measured, and in allowing the sleep interval to be  speci-
       fied 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 follow-
       ing 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  termi-
       nates 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  com-
       plete 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  encoun-
       ters  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 permit-
              ted 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 com-
       pletes, 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 sig-
       nal 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  dis-
       positions 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 deter-
       mine   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 4.15 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)