Re: problem with RPC over SSL and concurrency

Hi Jake,

although I don't understand exactly the way you are using RPC+SSL, there
is clearly a bug when operations are immediately canceled. I include the
patch into the svn version of ocamlnet. Thanks for reporting and fixing
the problem.

Gerd

Am Mittwoch, den 18.03.2009, 18:03 -0700 schrieb Jake Donham:
> Hi list,
> 
> I have a constellation of communicating RPC services. Each is
> implemented using Equeue cooperative threads. Within each service,
> there is a single client connection to each other service with which
> it must communicate, which is shared among the cooperative threads.
> The Rpc_client and Rpc_transport modules seem to be designed for this
> mode of use, and in fact this works fine over plain RPC. However, over
> SSL I get exceptions that suggest unsafe concurrent access (e.g.
> "#start_reading: already reading", among others).
> 
> Looking at Uq_ssl.ssl_mplex_ctrl, I see one thing that looks a bit
> suspicious: In start_reading, we call nonblock_operation, which queues
> a callback (using Unixqueue.once) that reads from the socket. But in
> cancel_reading, we don't remove the callback. So if we start reading
> and then cancel before the callback is called, it seems to me that the
> read still happens, and when_done is possibly called twice (once from
> cancel_reading and once from the start_reading action). Is this in
> fact a bug?
> 
> Thanks,
> 
> Jake
> 
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Gerd Stolpmann * Viktoriastr. 45 * 64293 Darmstadt * Germany 
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Apps built with the Adobe(R) Flex(R) framework and Flex Builder(TM) are
powering Web 2.0 with engaging, cross-platform capabilities. Quickly and
easily build your RIAs with Flex Builder, the Eclipse(TM)based development
software that enables intelligent coding and step-through debugging.
Download the free 60 day trial. http://p.sf.net/sfu/www-adobe-com