Filter chain behaviour on browser disconnection

Question

Hi
I'm trying to implement a filter that acts as a work queue. Here's the code I use in my filter:
// push a new worker to the queue, the queue will wait() if there are already enough active workers.
queue.push(this);
// out of the queue, let the chain process the request
chain.doFilter(request, response);
// inform queue that the current worker is done and the next queued worker can be released
queue.pop();
The code works fine with normal user activity, but if the user disconnects the page (presses stop or browses another link), the processing doesn't reach queue.pop(). I would like to somehow get information relayed to queue or filter that that "the browser disconnected", but I'm not sure if this possible.
From previous threads in this forum I just found techniques which used the browser to launch some event, but those aren't suitable in this case.
The only approach I've figured out would be to use a leaky queue implementation. The queue would leak a worker periodically if no workers have been released after a specified time. I'd definitely appreciate better solutions =)
I'm using the Orion application server 1.6.0b.

Answer 1

Hi
Yes, it works even when the browser is fully disconnected (I verified this from the firewall's connections). The filter doesn't intercept the disconnection, but instead it's guaranteed that the page gets fully rendered.
Currently I use the following approach:
1. try/catch around chain.doFilter(request, response); to catch any thrown exceptions in the filter chain or while page was rendered. The worker is released from the queue when the execution of the code gets back from doFilter() and any recieved exceptions are thrown upwards.
2. Leaky queue, which leaks workers if the above doesn't work for some reason
3. Since there might be other worker queues in use while rendering the page (which need to be freed in case of an error), they're stored to a Vector in request's context. Normally they're released after use, but if there's an error the error gets caught in 1. and there the vector is iterated releasing all work queues.