Don't forget to block asynchronous exception _before_ you fork in: > tid <- forkIO (someWorkToDo `finally` putMVar mv ())
Otherwise an asynchronous exception might be thrown to the thread _before_ the 'putMVar mv ()' exception handler is installed leaving your main thread in a dead-lock! You can use the threads library which correctly abstracts over this pattern: http://hackage.haskell.org/package/threads Regards, Bas On Wed, Sep 15, 2010 at 2:23 AM, Gregory Collins <g...@gregorycollins.net> wrote: > Mitar <mmi...@gmail.com> writes: > >> Hi! >> >> On Tue, Sep 14, 2010 at 11:46 PM, Bas van Dijk <v.dijk....@gmail.com> wrote: >>> Note that killing the main thread will also kill all other threads. See: >> >> Yes. But how does those other threads have time to cleanup is my question. > > What we do in Snap is this: the master thread has a catch handler which > catches the AsyncException generated by the call to killThread. When we > get this, we instruct any service loop threads to exit, and they all > wait for service threads to terminate (currently by sleep-polling a > connections table, which I should probably fix...). Then the master > thread exits by just returning. > > Note that I think the "main thread being killed kills all threads" issue > can be circumvented by using a little gadget like this: > > ------------------------------------------------------------------------ > someWorkToDo :: IO () > someWorkToDo = someStuff `catch` cleanupHandler > > main :: IO () > main = do > mv <- newEmptyMVar > tid <- forkIO (someWorkToDo `finally` putMVar mv ()) > > -- wait on thread to finish; any exception here is probably an > -- AsyncException, so kill the someWorkToDo master thread > -- yourself and wait on the mvar again > > takeMVar mv `catch` \(e::SomeException) -> do > killThread tid > takeMVar mv > ------------------------------------------------------------------------ > > At least, this is what we do in our webserver, and it seems to work > fine -- users complain about the delay involved in our slow cleanup > handler when they ctrl-c the server. :) > > G > -- > Gregory Collins <g...@gregorycollins.net> > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
