From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00
	autolearn=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!mx02.eternal-september.org!.POSTED!not-for-mail
From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: confusion about message passing between the tasks
Date: Sat, 25 Oct 2014 09:13:04 +0200
Organization: A noiseless patient Spider
Message-ID: <87lho4ei67.fsf@ludovic-brenta.org>
References: <d377c4f7-8c89-4b60-907d-f9151ae02721@googlegroups.com>
	<87tx2te2hz.fsf@ludovic-brenta.org>
	<f5f92033-cca6-4f9d-ab21-c031e2d7fe89@googlegroups.com>
Mime-Version: 1.0
Content-Type: text/plain
Injection-Info: mx02.eternal-september.org;
 posting-host="f51eff624ce5a87c6ebf9332dd27f01f";
	logging-data="31862"; mail-complaints-to="abuse@eternal-september.org";
	posting-account="U2FsdGVkX1+bAOwxoadDpG38GahrzDVj"
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux)
Cancel-Lock: sha1:Xa4r+oWUKN4jJDA10Mrn0OO27cc=
	sha1:+DjovPRqGvJKTVjpYs0P+Zrdwvc=
Xref: news.eternal-september.org comp.lang.ada:22719
Date: 2014-10-25T09:13:04+02:00
List-Id: <comp.lang.ada>

compguy45@gmail.com writes:
> In those directories all example are graphics example. Which directory
> is one that creates N tasks?

The directories 1..5 all contain different versions of the same
graphical program.

Version 1: no tasks.

Version 2: N tasks, race condition when multiple tasks want to draw
using a shared graphics context.

Version 3: race condition solved by placing the graphics context in a
protected object. But the problem now, with 10_000 tasks, is excessive
virtual memory consumption (8 MiB of stack per task), which luckily does
not translate into physical memory usage, at least on Linux.

Version 4: Introduce a task queue.  Now the number of tasks is
independent on the number of rectangles.  But there is still a problem;
a deadlock exists when one task A finds that there remains a rectangle
in the queue but another task B gets to dequeue it first.  Then A tries
to dequeue the last rectangle but waits forever as the queue is now
empty.  As a consequence the master task waits forever for A to
complete.

Version 5: deadlock solved by a select statement.

-- 
Ludovic Brenta.