clib package

packages/clib/demo/fork.pl

@@ -0,0 +1,33 @@
+/*  $Id$
+
+    Part of SWI-Prolog
+
+    Author:  Jan Wielemaker
+    E-mail:  jan@swi.psy.uva.nl
+    WWW:     http://www.swi.psy.uva.nl/projects/SWI-Prolog/
+    Copying: GPL-2.  See the file COPYING or http://www.gnu.org
+
+    Copyright (C) 1990-2001 SWI, University of Amsterdam. All rights reserved.
+*/
+
+:- use_module(library(unix)).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Simple demo illustrating the combination of   fork/1  and pipe/2 to make
+Prolog fork a child to do  some  work   and  get  back  when done. Using
+wait_for_input/3 you can make the  main   Prolog  task wait for multiple
+childs to return results.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+fork_demo(Result) :-
+	pipe(Read, Write),
+	fork(Pid),
+	(   Pid == child
+	->  close(Read),
+	    format(Write, '~q.~n', [hello(world)]),
+	    flush_output(Write),	% stream is fully buffered!
+	    halt
+	;   close(Write),
+	    read(Read, Result),
+	    close(Read)
+	).