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NAME
       nanosleep - high resolution sleep (REALTIME)


SYNOPSIS
       #include <time.h>

       int nanosleep(const struct timespec *rqtp, struct timespec *rmtp);


DESCRIPTION
       The  nanosleep()  function shall cause the current thread to be suspended from execution until either the
       time interval specified by the rqtp argument has elapsed or a signal is delivered to the calling  thread,
       and  its  action is to invoke a signal-catching function or to terminate the process. The suspension time
       may be longer than requested because the argument value is rounded up to an integer multiple of the sleep
       resolution  or  because  of  the  scheduling of other activity by the system. But, except for the case of
       being interrupted by a signal, the suspension time shall not be less than the time specified by rqtp,  as
       measured by the system clock CLOCK_REALTIME.

       The use of the nanosleep() function has no effect on the action or blockage of any signal.


RETURN VALUE
       If  the  nanosleep()  function  returns because the requested time has elapsed, its return value shall be
       zero.

       If the nanosleep() function returns because it has been interrupted by a signal, it shall return a  value
       of  -1  and  set  errno  to  indicate  the  interruption.  If the rmtp argument is non-NULL, the timespec
       structure referenced by it is updated to contain the amount  of  time  remaining  in  the  interval  (the
       requested  time  minus  the time actually slept). If the rmtp argument is NULL, the remaining time is not
       returned.

       If nanosleep() fails, it shall return a value of -1 and set errno to indicate the error.


ERRORS
       The nanosleep() function shall fail if:

       EINTR  The nanosleep() function was interrupted by a signal.

       EINVAL The rqtp argument specified a nanosecond value less than zero or greater than  or  equal  to  1000
              million.

       The following sections are informative.


EXAMPLES
       None.


APPLICATION USAGE
       None.


RATIONALE
       It  is  common  to  suspend  execution of a process for an interval in order to poll the status of a non-
       interrupting function. A large number of actual needs can be met with a simple extension to sleep()  that
       provides finer resolution.

       In  the  POSIX.1-1990 standard and SVR4, it is possible to implement such a routine, but the frequency of
       wakeup is limited by the resolution of the alarm() and sleep() functions. In 4.3 BSD, it is  possible  to
       write  such a routine using no static storage and reserving no system facilities. Although it is possible
       to write a function with similar functionality to sleep() using the remainder of the timer_*() functions,
       such  a  function  requires  the use of signals and the reservation of some signal number. This volume of
       IEEE Std 1003.1-2001 requires that nanosleep() be non-intrusive of the signals function.

       The nanosleep() function shall return a value of 0 on success and -1 on failure or if  interrupted.  This
       latter  case  is  different  from  sleep().  This  was done because the remaining time is returned via an
       argument structure pointer, rmtp, instead of as the return value.


FUTURE DIRECTIONS
       None.


SEE ALSO
       sleep() , the Base Definitions volume of IEEE Std 1003.1-2001, <time.h>


       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc  and  The  Open Group. In the event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard  is  the  referee  document.  The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .