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)