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threads - sync

This folder contains two simple multi-threading examples illustrating the use of the synchronized/1 predicate directive to cope with methods that have side effects.

The slow_print example was originally coded for a Rosetta Code contribution available at:

https://rosettacode.org/wiki/Mutex#Logtalk

This example should preferably be run from the top-level instead of as a notebook to observe the threads output.

When using XVM as the backend, this example must be run from the top-level interpreter.

Print Logtalk, Prolog backend, and kernel versions (if running as a notebook):

%versions

Start by loading the example:

logtalk_load(sync(loader)).

Slow print text (skip if running as a notebook):

(current_object(jupyter) -> true; slow_print::start).

<!-- abc 123 abc 123 abc 123 abc 123 abc ... -->

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

true. -->

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(_)).

<!-- false. -->

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

true. -->

threaded_call(nasty2::update_db(_)), threaded_call(nasty2::update_db(_)), threaded_call(nasty2::update_db(_)).

<!-- true. -->

threaded_exit(nasty2::update_db(X)), threaded_exit(nasty2::update_db(Y)), threaded_exit(nasty2::update_db(Z)).

<!-- X = 1 Y = 2 Z = 3

true. -->