NANOSLEEP(P)						     POSIX Programmer's Manual						      NANOSLEEP(P)

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_*() func-
       tions, 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>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- 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 .

IEEE
/The Open Group						       2003							      NANOSLEEP(P)