nanosleep

NANOSLEEP(2)		  Linux Programmer’s Manual		 NANOSLEEP(2)



NAME
       nanosleep - pause execution for a specified time

SYNOPSIS
       #include <time.h>

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

DESCRIPTION
       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 999 999
       999.

       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.

ERRORS
       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:

       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
	      999 999 999 or tv_sec was negative.

       EFAULT Problem with copying information from user space.

BUGS
       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.

       As some applications require much more precise pauses (e.g., in	order
       to  control some time-critical hardware), nanosleep is also capable of
       short high-precision pauses. If the process is scheduled under a real-
       time  policy  like  SCHED_FIFO  or SCHED_RR, then pauses of up to 2 ms
       will be performed as busy waits with microsecond precision.

CONFORMING TO
       POSIX.1b (formerly POSIX.4).

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



Linux 1.3.85			  1996-04-10			 NANOSLEEP(2)