NANOSLEEP(3P)                                       POSIX Programmer's Manual                                      NANOSLEEP(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

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 argu-
       ment 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 func-
       tion. 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 reserva-
       tion 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 Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                 NANOSLEEP(3P)