test client existence to terminate internal operations

[Cyril Lavy]

Hello,
I'm running a servlet which does some internal operations using much resources when a request is send. I have two problems: first, when someone clicks several times it sends several requests which can make the system busy for a long time, and second, if the session is closed (browser closed) or the operation is aborted on the client side, the servlet will continue to perform actions and sometimes block other users. So how can I :
- block several clicks from the same client.
- test client's existence.
- How can I declare the classes used in the operations so they can be heavily interrupted by the servlet if client's session is closed... Eternal Thanks to persons who can offer some help!

[Bear Bibeault]

This is a dupe of another topic (please don't post the same question twice). Please conduct any disucssion here.
bear