Path: utzoo!mnetor!uunet!nuchat!peter
From: peter@nuchat.UUCP (Peter da Silva)
Newsgroups: comp.sys.amiga
Subject: Re: IPC (1): Ports & Messages
Message-ID: <752@nuchat.UUCP>
Date: 9 Mar 88 02:29:45 GMT
References: <7412@agate.BERKELEY.EDU>
Organization: Public Access - Houston, Tx
Lines: 45
Keywords: InterProgram Communication, tools
Summary: A rationale for a message broker.

Good call on the task going away. For the case of the Browser messages I
suggested the other day I don't think that it's a problem.

(1) You can lock before sending any messages to the browser: there are
    only going to be two messages from you to it in any two-way conversation,
    anyway: 'ADDT' or 'ADDW' and 'DELT' and 'DELW'.

(2) You're supposed to tell Browser before you go away. If you always do
    this, but check that *it* hasn't gone away before doing so, there's not
    going to be a problem.

Now, as to a general message server. I don't like the idea of a reply port
being enything but a reply port, but you can always pass a port as part
of the message.

We can make the assumption that *it* isn't going to go away, ever. So:

You find it with the call FindPort("SERVER");

You can have two roles. You can be a master or a slave.

If you want to be a master, you send 'ADDM', your id, and a message port.
Server adds you to its list and replies. You are now registered. Before you
can go away you have to send it 'DELM'. It will then send 'DELM' to all
the slaves it knows you're talking to, and when it gets all their replies
it replies to you.

If you want to be a slave, you send 'ADDS', the master id, and a message port.
Server looks up the master in its list, adds you to the list of active slaves,
and forwards it your 'ADDS' message. The master's replies go back to you... the
server doesn't care. If the master doesn't exist, of course, it just replies
immediately with a failed status.

When you want to disconnect you send your master 'DELS' and it takes you out
of the list and forwards your message to the master. Once again the master
replies to you.

And of course if you ever get a 'DELM' message you reply to it and forget you
ever heard of the master.

This seems to have very little overhead. What do you all think?
-- 
-- a clone of Peter (have you hugged your wolf today) da Silva  `-_-'
-- normally  ...!hoptoad!academ!uhnix1!sugar!peter                U
-- Disclaimer: These aren't mere opinions... these are *values*.