#367: Infinite loops can hang Concurrent Haskell -------------------------------------+------------------------------------- Reporter: simonpj | Owner: ezyang Type: bug | Status: new Priority: lowest | Milestone: ⊥ Component: Compiler | Version: 6.4.1 Resolution: None | Keywords: scheduler Operating System: | allocation Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: Incorrect | Difficulty: Unknown result at runtime | Blocked By: Test Case: | Related Tickets: concurrent/should_run/T367, | concurrent/should_run/T367_letnoescape| Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by jberryman): As a user I'm having trouble understanding if the bug being discussed is the one reported. To be clear, is the following (very similar to #8521) an instance of this bug? Compiled with ghc 7.8.3 with `-O2 -threaded`, run with `+RTS -N` on a machine with two real cores. {{{ module Main where import Data.IORef import Control.Concurrent main = do r <- newIORef False putStrLn "About to fork" forkIO $ f r threadDelay 1000000 -- 1 second putStrLn "Why is this never printed?!" writeIORef r True -- and why do we never exit? f :: IORef Bool -> IO () f r = readIORef r >>= \b-> if b then print "Done" else f r }}} This wouldn't seem to have anything to do with whether `f`'s thread can be pre-empted or not, which is why I'm unsure. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/367#comment:39 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler