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From Emmanuel L├ęcharny <elecha...@gmail.com>
Subject [MINA 3] UDP support
Date Fri, 22 Mar 2013 09:53:29 GMT
Hi guys,

I'm currently working on the UDP support for MINA 3. Here is the way I
see the way to implement it, just tell me if you have any better idea,
suggestion, whatever.

First of all, there is a major difference between TCP and UDP : we don't
have to manage an OP_ACCEPT event for UDP. That means we just register
the socket on a selector for OP_READ events, and we process the incoming
data on the fly.

That has one direct consequence : we have to create the sessions based
on the remote address, and we have to assume that a request coming from
this remote address is associated with this session (in other words, if
the server does not close the session, and if we don't manage iddle
sessions, we will keep a session for a remote address forever).

So the algorithm would be somthing like :

select()
for each selectionKey selected because of an OP_READ event
  do
    find the associated session, based on the remote address
    if we get one,
      then process the data generating a messageReceived event
      else
        create a new session
        send a sessionCreated and sessionOpened event
        process the data generating a messageReceived event

This is a very rough description of how the main loop works.

Some few valuable bits :

1) We need one single thread to manage all the incoming messages. The
server will register the DatagramChannel on one single selector anyway...
2) As we use one single thread to process all the incoming messages, we
wil have to spread the load after having read the data. We will need an
executor for that (this is not mandatory, but this is the only way to
scale).
As a consequence, assuming we use a pool of thread to manage the events,
we need to guarantee that the messageReceived event is processed *after*
the sessionCreated and sessionOpened events.
3) One idea is to associate an event queue to each sessio. When we
create the session, we push three events in this queue : the
sessionCreated event, then the sessionOpened one, and finally, the
messageReceived event. Then we can peek a thread and let it process the
events.
4) Or we can associate one single thread to the session ( a bit like
what is done in MINA 2). It could make sense if we want to order the
event processing. I prefer the previous solution though.

So, wdyt ?

-- 
Regards,
Cordialement,
Emmanuel L├ęcharny
www.iktek.com 


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