Man Nanosleep en anglais
NANOSLEEP(2)               Linux Programmer's Manual              NANOSLEEP(2)



 

NAME


       nanosleep - high-resolution sleep

 

SYNOPSIS


       #include 

       int nanosleep(const struct timespec *req, struct timespec *rem);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       nanosleep(): _POSIX_C_SOURCE >= 199309L

 

DESCRIPTION






       nanosleep()  suspends  the execution of the calling thread until either
       at least the time specified in *req has elapsed, or the delivery  of  a
       signal  that triggers the invocation of a handler in the calling thread
       or that terminates the process.

       If the call is interrupted by a signal handler, nanosleep() returns -1,
       sets  errno  to EINTR, and writes the remaining time into the structure
       pointed to by rem unless rem is NULL.  The value of *rem  can  then  be
       used  to  call  nanosleep() again and complete the specified pause (but
       see NOTES).

       The structure timespec is  used  to  specify  intervals  of  time  with
       nanosecond precision.  It is defined as follows:

           struct timespec {
               time_t tv_sec;        /* seconds */
               long   tv_nsec;       /* nanoseconds */
           };

       The value of the nanoseconds field must be in the range 0 to 999999999.

       Compared to sleep(3)  and  usleep(3),  nanosleep()  has  the  following
       advantages:  it  provides  a higher resolution for specifying the sleep
       interval; POSIX.1 explicitly specifies that it does not  interact  with
       signals; and it makes the task of resuming a sleep that has been inter-
       rupted by a signal handler easier.

 

RETURN VALUE


       On  successfully  sleeping  for  the  requested  interval,  nanosleep()
       returns  0.   If the call is interrupted by a signal handler or encoun-
       ters an error, then it returns -1,  with  errno  set  to  indicate  the
       error.

 

ERRORS


       EFAULT Problem with copying information from user space.

       EINTR  The  pause has been interrupted by a non-blocked signal that was
              delivered to the thread.  The  remaining  sleep  time  has  been
              written into *rem so that the thread can easily call nanosleep()
              again and continue with the pause.

       EINVAL The value in the tv_nsec  field  was  not  in  the  range  0  to
              999999999 or tv_sec was negative.

 

CONFORMING TO


       POSIX.1-2001.

 

BUGS


   Old behavior
       In  order  to  support  applications requiring much more precise pauses
       (e.g., in order to control some  time-critical  hardware),  nanosleep()
       would handle pauses of up to 2 ms by busy waiting with microsecond pre-
       cision when called from a thread scheduled  under  a  real-time  policy
       like  SCHED_FIFO  or  SCHED_RR.   This special extension was removed in
       kernel 2.5.39, hence is still present in current 2.4 kernels,  but  not
       in 2.6 kernels.

       In  Linux  2.4,  if nanosleep() is stopped by a signal (e.g., SIGTSTP),
       then the call fails with the error EINTR after the thread is resumed by
       a  SIGCONT  signal.  If the system call is subsequently restarted, then
       the time that the thread spent in the  stopped  state  is  not  counted
       against the sleep interval.

 

NOTES


       If the interval specified in req is not an exact multiple of the granu-
       larity 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.

       The  fact  that nanosleep() sleeps for a relative interval can be prob-
       lematic if the call is repeatedly restarted after being interrupted  by
       signals,  since  the time between the interruptions and restarts of the
       call will lead to drift in the time when the sleep  finally  completes.
       This  problem  can be avoided by using clock_nanosleep(2) with an abso-
       lute time value.

       POSIX.1 specifies that nanosleep()  should  measure  time  against  the
       CLOCK_REALTIME  clock.   However,  Linux  measures  the  time using the
       CLOCK_MONOTONIC clock.   This  probably  does  not  matter,  since  the
       POSIX.1  specification  for  clock_settime()  says  that  discontinuous
       changes in CLOCK_REALTIME should not affect nanosleep():

              Setting the value of the  CLOCK_REALTIME  clock  via  clock_set-
              time()  shall have no effect on threads that are blocked waiting
              for a relative time service based upon this clock, including the
              nanosleep()  function;  ...   Consequently,  these time services
              shall expire when the requested relative interval elapses, inde-
              pendently of the new or old value of the clock.

 

SEE ALSO


       clock_nanosleep(2),  sched_setscheduler(2),  sleep(3), timer_create(3),
       usleep(3), time(7)

 

COLOPHON


       This page is part of release 3.05 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-06-24                      NANOSLEEP(2)