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                  More forays into multiprocessor programming
                                        
> From: "andrew cooke" <XXXXXXXXXXXXXXXXX>
> To: sean@conman.org
> Subject: Erlang bugs
> Date: Wed, 23 May 2007 08:12:35 -0400 (CLT)
> 
> Hi,
> 
> Found your page [1] (which references my Erlang Sudoku solver) via
> Technorati.
> 
> I can't for the life of me remember exactly what the cause was for the bug
> that you mention in that post, but I am pretty sure it wasn't to do with
> messaging or otherwise related to concurrency. A better explanation of why
> it was hard to track down is that the program is largely “indeterminate” in
> that the flow of control is unpredictable (because of random choices rather
> than concurrency itself).
> 
> However, when I added extra communication for the “community” version—
> http://www.acooke.org/cute/CommunityS0.html [2]—that did have serious
> deadlock issues that were directly related to concurrency. And I was
> surprised at how easy they were (ie how easy it was to introduce errors)—I
> had somehow convinced myself that Erlang made everything much safer. In
> retrospect its advantage is not that Erlang's message passing somehow
> magically avoids deadlocking, but that (1) it provides a clean framework
> for thinking about message passing that's nicely isolated and easy to read
> and manage and (2) assuming you stick to the pure functional parts of the
> language, state is already explicit and so easier to reason about.
> 
> Andrew
> 
> (Couldn't see a way to comment on the page, so emailing instead)
> 

Just another datapoint that writing concurrent programs, even in a langauge
like Erlang [3] which makes it easy, isn't easy.

[1] gopher://gopher.conman.org/0Phlog:2007/05/21.1
[2] http://www.acooke.org/cute/CommunityS0.html
[3] http://www.erlang.org/

Email Sean Conner at sean@conman.org

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