Hi,
the current implementation of filter's chain is associating this chain
to a service. In MINA 2, each session had a copy of this chain.
IMO, even if the default chain should be associated to the service, it
would be a better idea to create a copy of this chain for each created
session.
the rational behind this choice is that we then be able to add or remove
a filter from the chain dynamically for one specific session. One
obvious usage could be to add a logger when one would want to get some
traces for one session, and not for the whole service. We can also
imagine some other usages.
But it also has another direct advantage : currently, we compute the
next filter to process in the DefaultIoFilterController, where an
instance of the filter chain is stored. This DefaultIoFilterController
is associated with a service, and can then be used by more than one
selector, thus by more than one thread. That means we have to protect
the current chain position for a given selector by storing it into a
ThreadLocal. Access to the ThreadLocal values are way more expensive
than accessing a session's current position if it's a simple integer.
It would be easier if the controller was totally stateless, which would
be possible if the session was holding the filter's chain. Now, that
means we have to think about the way we should modify a chain for an
existing session. Obviously, if we store the current position in the
chain for a given session, we can't modify this position unless it's not
0, otherwise we might have some bad errors (ArrayOutOfBoundException,
for instance).
I still have to think a bit more about this, but I definitively think
that it's a better approach.
Thoughts ?
--
Regards,
Cordialement,
Emmanuel Lécharny
www.iktek.com
