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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