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From "Alan D. Cabrera" <l...@toolazydogs.com>
Subject Re: [MINA 3.0] Thougts about the selectors
Date Wed, 10 Feb 2010 21:28:11 GMT

On Feb 4, 2010, at 4:53 AM, Emmanuel Lecharny wrote:

> I have reviewed the way we use the Selector in MINA 2.0. Here are  
> some of the thoughts I have about teh way we use them for Sockets :
>
> We currently have a system built on top of three elements :
> - IoAcceptor on the server side
> - IoConnector on the client side
> - IoProcessor which are processing the messages received or sent
>
> IoAcceptor and IoConnector are just two sides of the same coin : a  
> IoService. The only difference is that the Connector initiates the  
> communication.
>
> Nio Sockets
> ----------------
> In order to deal with incoming connections, the IoAcceptor uses a  
> Selector on which are registered the ServerSocketChannel for the  
> OP_ACCEPT event. On the client side, we have the same Selector but  
> the ServerSocket is registered for the OP_CONNECT event.
>
> In both case, once the session is connected/accepted, the associated  
> Channel is attached to another Selector, itself associated with an  
> IoProcessor.
>
> Here, I'm questioning the fact that we use more than one Selector to  
> handle connect/accept  and read/write operations. The select()  
> operation is not specially costly, even if it does a lot of things :
> - deregister the canceled channels
> - each channel which has had some operation since the last select is  
> put to a set of selected keys
> - deregister the canceled channels again (for channel which has been  
> canceled while the step 2 was processed)
> - return the number of keys found ready in step 2
>
> but all in all, this is a fast operation, as it just reads some bit  
> fields to determinate if something has changed since the last  
> select. Even if we have one million registered keys in the selector,  
> first the number of active channel will be low, and second the  
> processing time for this step is very minimal compared to the  
> application processing time.
>
> Now, wouldn't it be better to have only one selector, and then  
> dispatch the tasks to some processor?
>
> On the server side, we have to deal with :
> - newly added sessions
> - recently closed sessions
> - incoming data
> - outgoing data
>
> On the client side, we have to deal with :
> - newly connected sessions
> - recently closed sessions
> - incoming data
> - outgoing data
>
> each of those tasks can be processed by a separate thread selected  
> in a thread pool. IMO, it may be better than the current  
> architecture where we have a pool of IoProcessor, each one of them  
> having its own Selector, and no thread to process the events. For  
> instance, if we have 3 IoProcessor (the default value for a dual  
> core processor), then we can only process 3 events in parallel.  
> Pretty inefficient...

I tried to follow the code for IoProcessor and my brain hurts.  :)   
Did I read correctly that the sessions are partitioned between N  
IoProcessors?  If so, seems kinda odd and I agree, what you propose  
seems more straightforward.


Regards,
Alan



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