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From André Warnier ...@ice-sa.com>
Subject Re: websockets questions
Date Thu, 04 Jul 2013 14:52:50 GMT
Mark Thomas wrote:
> On 04/07/2013 10:17, André Warnier wrote:
>> To me that means that at some point, there must be on the server side a
>> process or thread which is dedicated to this websocket client for as
>> long as it takes, and this process/thread in the meantime is no longer
>> available to process other HTTP requests.
>> (That's because the basic idea is that the "websocket application" on
>> the server side can keep sending messages asynchronously to the client -
>> and vice-versa - so I don't see how this can work with different
>> threads/processes on the server; but I'm not that smart, so it may be
>> that the implementation is smarter).
>> For that same reason, it would seem that the very concept of
>> "load-balancing" must be suspended once the websocket connection is
>> established.
> 
> The connection has to be kept open but you can use non-blocking IO to
> only allocate a thread to process data when there is data to process.
> 
> The exact behaviour varies between Tomcat 7 and Tomcat 8.
> 
> BIO 7 & 8 - 1 thread per connections, blocking IO, doesn't scale
> 
> NIO / APR 7 - 1 thread per currently processed frame, non-blocking
> between frames, scales better
> 
> NIO / APR 8 - threads only allocated where there is data to process,
> scales best

"data to process" meaning an entire websocket "message" I suppose ?

> 
> Note that JSR356 allows blocking writes. If the client or the server opt
> to send data using a blocking write then that will use a thread until
> the write completes.
> 
> Load-balancers should cope perfectly happily with this.
> 
> There is no upgrade or WebSocket support in AJP yet.
> 

Thanks for these precisions.

Another question while we're at it :
As I understand from the specs/docs, there are 2 kinds of messages : text or "blob".
And I found that there are 2 ways of reading that data, corresponding to these 2 types of

messages.
However, I do not find anywhere a function or method or call which would allow for example

the server-side application to find out in advance if the data currently available for 
reading is one or the other type.  Did I miss that somewhere, or do I misunderstand the 
specs/docs ?


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