#8235: Race condition in IO manager -------------------------------------+------------------------------------ Reporter: parcs | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: libraries/base | Version: 7.7 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: Runtime crash | Difficulty: Unknown Test Case: | Blocked By: Blocking: 910 | Related Tickets: -------------------------------------+------------------------------------ Comment (by parcs): This is what I think is happening: 1. The third call to `setNumCapabilities` causes the event manager on cap 1 to be restarted via `restartPollLoop`. 2. `restartPollLoop` forks a new poll loop. 3. `main` finishes and the RTS begins shutting down. 4. The RTS sends a die message to the timer manager. 5. The RTS flushes its capabilities' run queues. The timer-manager thread is run first. The timer manager reads the die message and shuts down the event managers, setting each event manager's state to `Dying`. 6. The original poll loop on cap 1 is run next. Its state variable reads `Dying`, so it shuts itself down. Its state variable is now `Finished`. 7. The new poll loop on cap 1 is finally run for the first time. Its state variable initially reads `Finished`, so it throws an error. Does this make sense? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8235#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler