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       nanosleep - pause execution for a specified time


       #define _POSIX_C_SOURCE 199309 #include <time.h>

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


       nanosleep()  delays  the execution of the program for at least the time
       specified in *req.  The function can return earlier  if  a  signal  has
       been  delivered to the process. In this case, it 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.

       The structure timespec is  used  to  specify  intervals  of  time  with
       nanosecond precision. It is specified in <time.h> and has the form

              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  advantage  of
       not  affecting  any  signals,  it is standardized by POSIX, it provides
       higher timing resolution, and it allows to continue a  sleep  that  has
       been interrupted by a signal more easily.


       In  case  of an error or exception, the nanosleep() system call returns
       -1 instead of 0 and sets errno to one of the following values:

       EFAULT Problem with copying information from user space.

       EINTR  The pause has been interrupted by a non-blocked signal that  was
              delivered  to  the  process.  The  remaining sleep time has been
              written  into  *rem  so  that  the  process  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.


       The current implementation of nanosleep() is based on the normal kernel
       timer  mechanism,  which  has  a  resolution  of  1/HZ s (i.e, 10 ms on
       Linux/i386 and 1 ms on  Linux/Alpha).   Therefore,  nanosleep()  pauses
       always for at least the specified time, however it can take up to 10 ms
       longer than specified until the process becomes runnable again. For the
       same  reason,  the value returned in case of a delivered signal in *rem
       is usually rounded to the next larger multiple of 1/HZ s.

   Old behaviour
       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
       precision when called from a process 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.


       POSIX.1b (formerly POSIX.4).


       sched_setscheduler(2), timer_create(2), sleep(3), usleep(3)