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Subject [jira] Commented: (GERONIMO-373) Percolate errors from SocketProtocol up the stack
Date Tue, 12 Oct 2004 19:51:51 GMT
The following comment has been added to this issue:

     Author: David Farb
    Created: Tue, 12 Oct 2004 12:51 PM

An explicit contract would be a better solution than the packet approach in my opinion, as
Craig said: 'The teardown signal object got special handling at each level, which actually
was a disadvantage, since it required an "if" statement to check the type of signal object,

This type of situation is better handled with an explicit method such as fail(), reserved
for that use. Then both the normal method (sendUp) and the failure method (fail) are simpler.
I would add the exception (if any) to the fail method just for documentation purposes:

   public void fail(Throwable throwable);

Once the fail 'signal' gets to the top of the protocol stack, other means such as custom wrapper
objects can be used to percolate the information to other parts of the server.

The 'Command' pattern seems like it ought to fit here, but the number of different classes
of server objects looks like a problem.

As far as I can tell, I may be the only one using this code at the moment, so I would be happy
to build the fix. I will probably wait until next week to allow more time for feedback and

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Here is an overview of the issue:
        Key: GERONIMO-373
    Summary: Percolate errors from SocketProtocol up the stack
       Type: Improvement

     Status: Unassigned
   Priority: Major

    Project: Apache Geronimo

   Reporter: David Farb

    Created: Tue, 12 Oct 2004 9:42 AM
    Updated: Tue, 12 Oct 2004 12:51 PM
Environment: All environments

Description: does not percolate a client error or exception up the
protocol stack when the client disconnects.

When serviceRead in SocketProtocol gets an IOException or some other error, the socketChannel
is closed, but the up protocol is not informed.

Calling the teardown method of the up protocol is probably not an appropriate way to handle
these exceptions. The teardown method should be called by the creator of the protocol stack.
Instead, the exception/error should percolate up the protocol stack to the creator (via some
sort of callback mechanism) which should then remove the stack and associated information
from the server environment. 

Either a new method reserved for this could be defined in the Protocol interface (up.handleException(Throwable
t)) or sending a null, empty or specially marked packet via up.sendUp(UpPacket upPacket) could
be implemented.

Since in most cases the server is waiting for a client response, if the client goes away,
server components need to be informed of this fact so the server side objects can be cleaned
up. There is usually no way to recover these objects, hence they are a memory leak.

I would be happy to submit a fix for this, but I would appreciate feedback on the most appropriate
way to do it.

David Farb

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