Re: [Haskell-cafe] Cleaning up threads
Note that killing the main thread will also kill all other threads. See: http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/Control-Concurrent.html#11 You can use my threads library to wait on a child thread and possibly re-raise an exception that was thrown in or to it: http://hackage.haskell.org/package/threads Regards, Bas On Mon, Sep 13, 2010 at 5:32 AM, Mitar mmi...@gmail.com wrote: Hi! I run multiple threads where I would like that exception from any of them (and main) propagate to others but at the same time that they can gracefully cleanup after themselves (even if this means not exiting). I have this code to try, but cleanup functions (stop) are interrupted. How can I improve this code so that this not happen? module Test where import Control.Concurrent import Control.Exception import Control.Monad thread :: String - IO ThreadId thread name = do mainThread - myThreadId forkIO $ handle (throwTo mainThread :: SomeException - IO ()) $ -- I want that possible exception in start, stop or run is propagated to the main thread so that all other threads are cleaned up bracket_ start stop run where start = putStrLn $ name ++ started stop = forever $ putStrLn $ name ++ stopped -- I want that all threads have as much time as they need to cleanup after themselves (closing (IO) resources and similar), even if this means not dying run = forever $ threadDelay $ 10 * 1000 * 1000 run :: IO () run = do threadDelay $ 1000 * 1000 fail exit main :: IO () main = do bracket (thread foo) killThread $ \_ - bracket (thread bar) killThread $ \_ - bracket (thread baz) killThread (\_ - run) Mitar ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cleaning up threads
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. You can use my threads library to wait on a child thread and possibly re-raise an exception that was thrown in or to it: Thanks. Will look into it. Mitar ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cleaning up threads
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
Re: [Haskell-cafe] Cleaning up threads
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
Re: [Haskell-cafe] Cleaning up threads
Bas van Dijk v.dijk@gmail.com writes: 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! Good catch, thank you, G -- Gregory Collins g...@gregorycollins.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cleaning up threads
Also don't forget to unblock asynchronous exceptions inside 'someWorkToDo' otherwise you can't throw exceptions to the thread. Note that 'finally' unblocks asynchronous exceptions but I consider this a bug. In the upcoming base library this is fixed[1] but I would advise to fix the code right now to not be surprised later. Also note that the threads library correctly unblocks asynchronous exceptions when necessary. Regards, Bas [1] http://hackage.haskell.org/trac/ghc/ticket/4035 On Wed, Sep 15, 2010 at 7:38 AM, Gregory Collins g...@gregorycollins.net wrote: Bas van Dijk v.dijk@gmail.com writes: 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! Good catch, thank you, G -- Gregory Collins g...@gregorycollins.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
