On Sun, Apr 17, 2011 at 20:26, Edward Z. Yang
This is a fairly nontrivial problem. First off, let me tell you what you do not /actually/ want to happen: you don't want the OS level thread performing the foreign call to actually be killed...
From this I gather, one can not generally kill Haskell threads while they are in the midst of foreign calls. I guess interrupting execution to terminate the program is special since you don't expect anything to work properly afterward.
If the asynchronous API has the ability to cancel a query given some handler, you instead want to set up a custom kill thread function that checks if a thread has an active query and then performs another FFI call to perform that cancellation.
It turns out the PGcancel exists for this purpose. Is it safe and reasonable to make query cancellation a ThreadKilled handler in the query thread? I gather I need to write the busy loop for polling for data in Haskell. Although libpq has a procedure -- PGgetResult -- that polls for data, it would not respond to killThread. -- Jason Dusek () ascii ribbon campaign - against html e-mail /\ www.asciiribbon.org - against proprietary attachments