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Date: -- (:)
From: Costin Stefan <costins@a...>
Subject: Re: [Caml-list] Thread and sockets
David Mentre wrote:

> Hello,
>
> I'm building a Caml client/server program using posix threads and
> sockets. Right now, I have 3 threads:
>
>  1. normal thread for user computation
>
>  2. a thread doing a blocking call to Unix.accept to setup new
>     connections
>
>  3. a thread doing a blocking call to Thread.select (with infinite
>     timeout) to get messages on opened connections

First of all read the man pages for read/write/select of the C system calls.

>
>
> I've observed that my design is bad and I have several race
> conditions. Worse problems are when I open and close connections. For
> example, if thread (3) is blocked and a new connection is opened by
> thread (2), thread (3) won't read new messages. I have similar problems
> when sockets are closed. How to do it properly?

A better approach (for thread 3) is :
do forever{
1. a select with a timeout.
2. When the select exit see if have data available or timeout occurred !
3. Then you can test if exists new accepted connections.
}


>
>
> I think I should open a dedicated thread for each new socket [1].
> However I don't know how to stop a thread waiting inside a blocking
> call. What happens if the remote part close the socket where a thread is
> doing a select (or a read). Does this thread get an exception?

When you try to read from a socket and the remote part close the socket
you will receive a SIGPIPE signal (try to handle this ;-) )

>
>
> I also don't know how to stop cleanly thread (2). Should another thread
> close the socket where thread (2) is doing an Unix.accept on?
>
> I would accept with pleasure any advice on this subjet.
>
> Best regards,
> david
>
> [1] At first, I did not choose this design to avoid creating zillions of
>     new posix (i.e. kernel, on Linux) threads.

Who many simultaneous connections do you want to handle ?
Is enough a single thread for this ?

>
> --
>  David.Mentre@inria.fr
>  Opinions expressed here are only mine.
> -------------------
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