[Simh] Trouble with sockets

[SPC]

I don't receive mails from this list from days ago. In fact I was wondering
why.

Sergio


2009/6/17 Robert Jarratt <robert.jarratt at ntlworld.com>

>  I sent the message below about 10 days ago and could not understand why
> it failed to appear. I have since worked out what the problem was so I no
> longer need an answer, except to the question of why it took so long to
> appear?
>
>
>
> Thanks
>
>
>
> Rob
>
>
>
> *From:* simh-bounces at trailing-edge.com [mailto:
> simh-bounces at trailing-edge.com] *On Behalf Of *Robert Jarratt
> *Sent:* 06 June 2009 13:57
> *To:* simh at trailing-edge.com
> *Subject:* [Simh] Trouble with sockets
>
>
>
> I am trying to add a new point-to-point communications device to SIMH. I am
> using sockets as the underlying communications mechanism and the routines in
> sim_sock.c in particular. The polled nature of SIMH seems to be causing me
> some intermittent problems however.
>
>
>
> Background: I use two separate connections for each device, one for the
> device to send data, and one for it to receive data. This is because I want
> each device to be the same, otherwise for each point-to-point pair I would
> have to configure one to be passive and listen for connections and the other
> to be active, and I cannot necessarily anticipate which one will need to
> communicate first. Essentially I need full-duplex. This means each device is
> configured with its own receive port and the port of the remote device to
> which it is supposed to connect.
>
>
>
> On the receive side I have to poll for incoming connections because I do
> not know if the remote machine is even running, so I cannot wait for an
> incoming connection as this would block the whole virtual machine. On the
> transmit side I have to poll for an outgoing connection for largely the same
> reason.
>
>
>
> The problem: Sometimes the software gets itself into a state where the
> transmit side starts a connection and then gets a WSAENOTCONN, and at the
> same time the receive side gets a WSAECONNRESET. I think this is because of
> the non-blocking nature of the sockets, required because of the polled
> nature of SIMH. What seems to be happening is that the transmit side starts
> a connection, the receive side sees it but in that time the transmit side
> has decided that the receiver is not going to connect so it closes the
> connection and then the receive side sees it as disconnected.
>
>
>
> The question: I am doing the development on Windows, and there are several
> mechanisms I could use to allow for asynchronous notification of an incoming
> connection. The problem is that I am not sure how portable these are to
> other environments.
>
>
>
> I have tried making the sim_connect_sock block instead, but I think that
> when the receive side is not running this would cause a huge slow-down on
> the sending virtual machine (while it waits for the connect to fail); and at
> the moment sim_connect_sock also prints an error message (WSAECONNREFUSED)
> for each failed connect poll as a result of the receive side not being
> present.
>
>
>
> I am looking for suggestions for the best way to deal with this.
>
>
>
> Thanks
>
>
>
> Rob
>
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>
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