Hi, comments inline On Fri, Mar 22, 2013 at 6:22 PM, Jeff MAURY <jeffma...@jeffmaury.com> wrote:
> I don't think we should try to map the session concept on top of UDP. It > think this is something that should be done at the user level. > The whole MINA API is bound the the IoSession how you see UDP servers without the IoSession ? Directly read/write on the service ? with only one filter chain ? Let me explain a little > Using UDP, as a server, the only information you have is there is one > message (and not packet) from this address. > If you map the session concept based on the remote address, I don"t see how > this can be handled as UDP does not guaranty the order of the messages. > But you can add some IoFilter for doing that: reordering, retransmission, congestion control (well only if you really want to reimplements TCP on top of UDP :) So if you want to implement a session, this can be done only on the user > level where you must have something that will mimic what TCP does > (ordering, retransmission,...). > It's perhaps simply a session but with the caracteristic of UDP : not in order, loss of some datagram.. > So I would opt for a session-less solution but allowing to retrieve > information needed (I think this is restricted to the remote socket > address) to implement sessions on the user level. > > WDYT ? > Jeff > > > > On Fri, Mar 22, 2013 at 10:53 AM, Emmanuel Lécharny <elecha...@gmail.com > >wrote: > > > 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 Lécharny > > www.iktek.com > > > > > > > -- > Jeff MAURY > > > "Legacy code" often differs from its suggested alternative by actually > working and scaling. > - Bjarne Stroustrup > > http://www.jeffmaury.com > http://riadiscuss.jeffmaury.com > http://www.twitter.com/jeffmaury >
