Logtalk 2.29.1 files.

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Logtalk/examples/threads/sync/NOTES.txt

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+=================================================================
+Logtalk - Object oriented extension to Prolog
+Release 2.29.1
+
+Copyright (c) 1998-2006 Paulo Moura.  All Rights Reserved.
+=================================================================
+
+
+To load this example and for sample queries, please see the SCRIPT file.
+
+This folder contains a simple multi-threading example illustrating the 
+use of the "synchronized" predicate directive to cope with methods that 
+have side-effects.
+
+The object defined in the example source file, "sync.lgt", defines a 
+predicate named waste_time/0 that is used to delay the execuion of goals 
+in order to better illustrate the semantics of the "synchronized" predicate 
+directive. This predicate uses a counter that you might need to adjust, 
+depending on your Prolog compiler and computer performance.

Logtalk/examples/threads/sync/SCRIPT.txt

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+=================================================================
+Logtalk - Object oriented extension to Prolog
+Release 2.29.1
+
+Copyright (c) 1998-2006 Paulo Moura.  All Rights Reserved.
+=================================================================
+
+
+% start by loading the loading the example:
+
+| ?- logtalk_load(sync(loader)).
+...
+
+
+% send three asynchronous messages whose corresponding methods perform output operations:
+
+| ?- threaded_ignore(nasty1::io(alpha)), threaded_ignore(nasty1::io(digit)), threaded_ignore(nasty1::io(alpha)).
+
+a0ab1bc2c3ddefef45gg6hh7ii8jkjk9
+llmmnnopopqqrrsstztzyyxxwwuv
+uv
+
+Yes
+
+
+% send three asynchronous messages whose corresponding methods perform database updates
+% (this may or may not work, most likely will throw an exception):
+
+| ?- threaded_ignore(nasty1::update_db(_)), threaded_ignore(nasty1::update_db(_)), threaded_ignore(nasty1::update_db(_)).
+
+No
+
+
+% the best solution is to declare predicates that need to be thread synchronized as "synchronized",
+% as exemplified in object "nasty2":
+
+| ?- threaded_ignore(nasty2::io(alpha)), threaded_ignore(nasty2::io(digit)), threaded_ignore(nasty2::io(alpha)).
+
+abcdefghijklmnopqrstzyxwuv
+0123456789
+abcdefghijklmnopqrstzyxwuv
+
+Yes
+
+
+| ?- threaded_call(nasty2::update_db(_)), threaded_call(nasty2::update_db(_)), threaded_call(nasty2::update_db(_)).
+
+Yes
+
+| ?- threaded_exit(nasty2::update_db(X)), threaded_exit(nasty2::update_db(Y)), threaded_exit(nasty2::update_db(Z)).
+
+
+X = 1
+Y = 2
+Z = 3 
+
+Yes

Logtalk/examples/threads/sync/loader.lgt

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+
+:- initialization(
+	logtalk_load(
+		sync)). 
+
+/*
+If you intend to use the FOP XSL:FO processor for generating PDF documenting
+files, comment the directive above and uncomment the directive below
+
+:- initialization(
+	logtalk_load(
+		sync, [xmlsref(standalone)])).
+*/

Logtalk/examples/threads/sync/sync.lgt

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+
+:- object(nasty1).
+
+	:- info([
+		version is 1.1,
+		author is 'Paulo Moura',
+		date is 2006/11/26,
+		comment is 'Simple example for illustrating the problems with lack of thread synchronization when calling methods with side-effects.']).
+
+	:- threaded.
+
+	:- public(update_db/1).
+	:- mode(update_db(-integer), one).
+	:- info(update_db/1, [
+		comment is 'Perform a database update with a long delay between retracting the old information and asserting the new one.',
+		argnames is ['New']]).
+
+	:- private(db/1).
+	:- dynamic(db/1).
+
+	:- public(io/1).
+	:- mode(io(+atom), one).
+	:- info(io/1, [
+		comment is 'Write some characters to the standard output stream with a long delay between each write operation.',
+		argnames is ['Chars']]).
+
+	db(0).
+
+	update_db(New) :-
+		retract(db(Old)),
+		waste_time,
+		New is Old + 1,
+		waste_time,
+		assertz(db(New)).
+
+	io(alpha) :-
+		write(a), waste_time, write(b), waste_time, write(c), waste_time, write(d), waste_time, write(e),
+		write(f), waste_time, write(g), waste_time, write(h), waste_time, write(i), waste_time, write(j),
+		write(k), waste_time, write(l), waste_time, write(m), waste_time, write(n), waste_time, write(o),
+		write(p), waste_time, write(q), waste_time, write(r), waste_time, write(s), waste_time, write(t),
+		write(z), waste_time, write(y), waste_time, write(x), waste_time, write(w), waste_time, write(u),
+		write(v), nl.
+
+	io(digit) :-
+		write(0), waste_time, write(1), waste_time, write(2), waste_time, write(3), waste_time, write(4),
+		write(5), waste_time, write(6), waste_time, write(7), waste_time, write(8), waste_time, write(9), nl.
+
+	waste_time :-
+		between(1, 10000, _),
+		fail.
+	waste_time.
+	
+	between(Lower, _, Lower).
+	between(Lower, Upper, Integer) :-
+		Lower < Upper,
+		Next is Lower + 1,
+		between(Next, Upper, Integer).
+
+:- end_object.
+
+
+:- object(nasty2).
+
+	:- info([
+		version is 1.1,
+		author is 'Paulo Moura',
+		date is 2006/11/26,
+		comment is 'Simple example for using the "synchronized" predicate directive for multi-threading methods with side-effects.']).
+
+	:- threaded.
+
+	:- public(update_db/1).
+	:- synchronized(update_db/1).
+	:- mode(update_db(-integer), one).
+	:- info(update_db/1, [
+		comment is 'Perform a database update with a long delay between retracting the old information and asserting the new one.',
+		argnames is ['New']]).
+
+	:- private(db/1).
+	:- dynamic(db/1).
+
+	:- public(io/1).
+	:- synchronized(io/1).
+	:- mode(io(+atom), one).
+	:- info(io/1, [
+		comment is 'Write some characters to the standard output stream with a long delay between each write operation.',
+		argnames is ['Chars']]).
+
+	db(0).
+
+	update_db(New) :-
+		retract(db(Old)),
+		waste_time,
+		New is Old + 1,
+		waste_time,
+		assertz(db(New)).
+
+	io(alpha) :-
+		write(a), waste_time, write(b), waste_time, write(c), waste_time, write(d), waste_time, write(e),
+		write(f), waste_time, write(g), waste_time, write(h), waste_time, write(i), waste_time, write(j),
+		write(k), waste_time, write(l), waste_time, write(m), waste_time, write(n), waste_time, write(o),
+		write(p), waste_time, write(q), waste_time, write(r), waste_time, write(s), waste_time, write(t),
+		write(z), waste_time, write(y), waste_time, write(x), waste_time, write(w), waste_time, write(u),
+		write(v), nl.
+
+	io(digit) :-
+		write(0), waste_time, write(1), waste_time, write(2), waste_time, write(3), waste_time, write(4),
+		write(5), waste_time, write(6), waste_time, write(7), waste_time, write(8), waste_time, write(9), nl.
+
+	waste_time :-
+		between(1, 100000, _),
+		fail.
+	waste_time.
+	
+	between(Lower, _, Lower).
+	between(Lower, Upper, Integer) :-
+		Lower < Upper,
+		Next is Lower + 1,
+		between(Next, Upper, Integer).
+
+:- end_object.