On Tue, Nov 9, 2010 at 5:37 PM, Mitar <mmi...@gmail.com> wrote: > Why is ThreadKilled not displayed by RTS when send to thread (and > unhandled), but any other exception is?
A ThreadKilled exception is not printed to stderr because it's not really an error and should not be reported as such. It is also clear how to handle a ThreadKilled: just abort the thread and silently terminate. All other exceptions raised in or thrown to the thread which are not handled by the thread itself should be considered errors and reported as such. To see what happens under the hood look at the implementation of forkIO by clicking on the 'Source' link next to the type signature: http://hackage.haskell.org/packages/archive/base/4.2.0.2/doc/html/Control-Concurrent.html#v%3AforkIO The 'action_plus' that is forked catches all exceptions and handles them with childHandler: ... where action_plus = catchException action childHandler childHandler in turn calls real_handler to handle the exception but registers an exception handler so that exceptions raised by the real_handler are handled again recursively: childHandler :: SomeException -> IO () childHandler err = catchException (real_handler err) childHandler Now real_handler handles the exceptions BlockedIndefinitelyOnMVar, BlockedIndefinitelyOnSTM and ThreadKilled by just returning. All other exceptions are reported: real_handler :: SomeException -> IO () real_handler se@(SomeException ex) = -- ignore thread GC and killThread exceptions: case cast ex of Just BlockedIndefinitelyOnMVar -> return () _ -> case cast ex of Just BlockedIndefinitelyOnSTM -> return () _ -> case cast ex of Just ThreadKilled -> return () _ -> case cast ex of -- report all others: Just StackOverflow -> reportStackOverflow _ -> reportError se > For example, I am using custom exceptions to signal different kinds of > thread killing. Based on those my threads cleanup in different ways. > But after they cleanup they keep "running". Not really running as > their computations were interrupted. But simply hanging there. And if > then new custom exception arrives it is not handled anymore (as it is > after my normal exception handlers already cleaned everything) and it > is printed to stderr. What do you mean by "hanging there". Are they blocked on an MVar? > Now I added "`finally` throwIO ThreadKilled" at the end of my cleanup > computations to really kill the thread. So that possible later > exceptions are not delivered anymore. That shouldn't be necessary. If the cleanup action is the last action of the thread then the thread will terminate when it has performed the cleanup. > Why it is not so that after all computations in a thread finish, > thread is not killed/disposed of? It actually should. I think any other behavior is a bug. It would help if you could show us your code (or parts of it). Regards, Bas _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
