PROLOG

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

NAME

       nanosleep — high resolution sleep

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). The rqtp and rmtp arguments can point to the same  object.
       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 thread 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
       POSIX.1‐2017 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

       clock_nanosleep(), sleep()

       The Base Definitions volume of POSIX.1‐2017, <time.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 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 .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                     NANOSLEEP(3POSIX)