Do you even have any idea what Forum you're posting to? Your question doesn't have anything even vaguely to do with OpenACS or even web/db in general.
As for your question itself, basically, RTFM.
For POSIX threads there is generally no way to forcibly kill a thread. If you want a thread to die, you must arrange for the thread to stop what's it's doing and exit on its own. Various unix Non-POSIX thread APIs do sometimes provide a forcible kill function. On MS Windows, I've no idea.