1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        jan@swi-prolog.org
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2022, SWI-Prolog Solutions b.v.
    7    All rights reserved.
    8
    9    Redistribution and use in source and binary forms, with or without
   10    modification, are permitted provided that the following conditions
   11    are met:
   12
   13    1. Redistributions of source code must retain the above copyright
   14       notice, this list of conditions and the following disclaimer.
   15
   16    2. Redistributions in binary form must reproduce the above copyright
   17       notice, this list of conditions and the following disclaimer in
   18       the documentation and/or other materials provided with the
   19       distribution.
   20
   21    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   22    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   23    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   24    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   25    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   26    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   27    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   28    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   29    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   31    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   32    POSSIBILITY OF SUCH DAMAGE.
   33*/
   34
   35:- module(unix_sched, []).   36:- use_foreign_library(foreign(sched)).   37:- if(current_predicate(setpriority/3)).   38:- export(setpriority/3).   39:- export(getpriority/3).   40:- endif.   41
   42/** <module> Access process scheduling
   43
   44This library provides an interface to  the process scheduling facilities
   45of the operating system. It is based   on  the sched(7) manual page from
   46Linux.
   47*/
   48
   49
   50%!  setpriority(+Which, +Who, +Priority) is det.
   51%!  getpriority(+Which, +Who, +Priority) is det.
   52%
   53%   Get/set the priority of a single process   or set of processed. Note
   54%   that on Linux threads are similar   to  processes and this interface
   55%   also applies to threads. The PID of   a  Prolog thread is accessible
   56%   through thread_property/2.  Which is one of
   57%
   58%     - process
   59%       Specify a single process/thread.  Who is the PID of the process.
   60%     - pgrp
   61%       Specify a _process group_. Who is the process group indentifier.
   62%       Currently SWI-Prolog has no interface to process groups.
   63%     - user
   64%       Specify all processes owned by a user.  Who is the numeric
   65%       user id of the target user.
   66%
   67%   Priority is the _nice_ value of the process and is an integer in the
   68%   range -20..20, where lower numbers denote a higher priority. Who can
   69%   be `0` (zero) to specify the calling process, process group or user.
   70%
   71%   Please consult the scheduler documentation  of your operating system
   72%   before  using  setpriority/3.  Unix  systems  generally  schedule  a
   73%   process at a given priority  only  if   there  is  no process with a
   74%   higher priority (lower nice value) in _runnable_ state.
   75%
   76%   For example, to lower the priority of the `gc` thread we can use the
   77%   call below.  Note that this may cause GC to never run.
   78%
   79%   ```
   80%   ?- thread_property(gc, system_thread_id(PID)),
   81%      setpriority(process, PID, 5).
   82%   ```
   83%
   84%   @error existence_error(Which, Who)
   85%   @error permission_error(setpriority, Which, Who)