#5553: sendWakeup error in simple test program with MVars and killThread -------------------------------------+------------------------------------- Reporter: bit | Owner: Type: bug | Status: new Priority: high | Milestone: 7.4.2 Component: Runtime System | Version: 8.0.1 Resolution: | Keywords: Operating System: Linux | Architecture: x86 Type of failure: Incorrect result | Test Case: at runtime | Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by basvandijk): * cc: basvandijk, simonmar (added) * status: closed => new * version: 7.2.1 => 8.0.1 * resolution: worksforme => * owner: tibbe => Comment: In a program at work I get exactly the same error. I'm on '''GHC-8.0.1'''. I'm using Don Stewarts [http://hackage.haskell.org/package/ghc-gc-tune ghc-gc-tune] to find the optimal GC settings for a server program. `ghc- gc-tune` expects the program to terminate. Since it's a server this doesn't happen. To fix this I wrap the program in `timeout --preserve- status 5` to terminate the server after 5 seconds. `ghc-gc-tune` will run the program many times with different `-H` and `-A` settings. Among other things, the program forks a thread which basically does the same thing as the `serverThread` of the OP: {{{ tid <- forkIO $ forever $ threadDelay 5000000 }}} The program ends with installing a signal handler for SIGTERM which will unlock a lock that the program is waiting on. Finally the forked thread is killed: {{{ lock <- newEmptyMVar installHandler sigTERM (Catch $ putMVar lock ()) (Just fullSignalSet) takeMVar lock killThread tid }}} I believe the `sendWakeup` exception is thrown in `threadDelay`. I'm trying to reduce to program so it doesn't contain any proprietary code but so far I'm not succeeding. It appears that [https://github.com/ghc/ghc/blob/ghc-8.0/libraries/base/GHC/Event/TimerManage... closeControl] is called before [https://github.com/ghc/ghc/blob/ghc-8.0/libraries/base/GHC/Event/TimerManage... wakeManager]. Could it be that the `state` IORef is [https://github.com/ghc/ghc/blob/ghc-8.0/libraries/base/GHC/Event/TimerManage... finalized] before we run `wakeManager`? If so, how can we ensure the garbage collector treats the IORef as reachable until after `wakeManager`? Maybe writing to it, as in: {{{ wakeManager :: TimerManager -> IO () wakeManager mgr = do sendWakeup (emControl mgr) atomicWriteIORef (emState mgr) $ \x -> (x, ()) }}} ? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/5553#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler