[Catalyst] How to detect cancelled requests?

[Stuart Watt]

Hi all,

Has anyone found a neat way of detecting and handling cancelled 
requests? We have a Catalyst app that dynamically generates SQL queries 
for part of its search, some of which are long and complex, and users 
are able to create queries that can take minutes to execute. This is OK, 
except that we need users to be able to cancel those requests through 
the browser.

To add complexity to this, we are using IIS (client specification) as 
the front end, although we are trying to get a FastCGI rather than CGI 
(with ActiveState's PerlEx) engine in place. We're doing this because we 
had to use our own Perl, simply because we were getting too many 
DBI-based memory leaks in the ActivePerl and Strawberry for our indexing 
system to be able to function effectively. (Essentially, this is a 
large-scale IR type application).

The Perl we use is not threaded, essentially a "5.10 with all the 
patches as of September 2008", although I'd be happy to make it threaded 
if that would help. As far as I can tell, alarm is just about capable of 
cancelling long-running database queries, and with polling, the database 
no longer seems to be the issue. However, rendering the results can take 
a while, and IIS seems to choose not to inform anyone (or us, at least) 
when the user cancels a request and the connection close is initiated.

Does anyone have any experience or recommendations?

All the best
Stuart
--
Stuart Watt
swatt at infobal.com