Subj : Re: Can long blocking tasks scale?
To   : comp.programming.threads,comp.parallel
From : Markus Elfring
Date : Tue Sep 06 2005 11:22 pm

[c.p. moderator back.]

Hans Malherbe wrote:
> What if your Windows server has to call a service that takes "long" and
> you need to make every effort to make it scale to as many concurrent
> requests as possible?

Are you sure that this kind of session management was not packaged into
a software library before?


> The problem is that the called service is a "black box" (mainframe
> program) which cannot be divided into smaller bits.

Do you know how satellite communication to the moon, mars or any other planets
and stars is organized with its noticeable transmission times?


> Currently every request consumes a thread which is mostly busy doing
> nothing but wait.

Did you try alternative techniques for the multiplexing of the processing?
Which approaches from other client/server APIs can be reused?


> Assuming the called service takes 40 seconds to respond with a request
> rate of 20 per second, we'll need to create 800 threads before the
> first ones start to return.
>
> It seems silly to hit the wall at 50 requests per second (2000 threads
> with 1 MB stack reserved per thread on Windows 2000 Server) when
> essentially they are all just waiting instead of doing.

How much can you decrease the stack size for your application?


> One proposed solution was to have the client make the request and drop
> the connection after which the client will poll to retrieve the result.
> The server thread will request from the "black box" and exit. The
> problem with this is that the "black box" must change significantly.

Are there any chances for an asynchronous (non-blocking) and bidirectional
communication protocol on the application layer?


> Complexity aside, how does this solution stack up against the
> alternative of one thread per request?

Are thread pools an useable option to manage any waiting queues in your case?


> Am I even asking the right questions?

Would you like to consider a cooperation with a message or notification service
like the tool "http://www.xmlblaster.org/"?

Regards,
Markus

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