#13330: forkIO has inconsistent behavior under optimization -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Core | Version: 8.1 Libraries | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Troubleshooting the T4030 failure in SimonPJ's early-inline branch, Reid and I discovered that the problem showed up when the argument to `forkIO` was obviously bottom. He came up with a tiny test case that fails without Simon's changes: {{{#!hs main = forkIO undefined >> threadDelay 1000000 }}} It looks like the trouble is in the definition of `forkIO`: {{{#!hs forkIO :: IO () -> IO ThreadId forkIO action = IO $ \ s -> case (fork# action_plus s) of (# s1, tid #) -> (# s1, ThreadId tid #) where action_plus = catchException action childHandler }}} This seems to run into the trouble with `catchException` and strictness explained in `GHC.IO`. It would appear that the conservative fix would be to replace `catchException` with `catch`. Personally, I find it a bit surprising that `forkIO` doesn't force its `IO` argument before forking, but changing that behavior could break working code. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13330 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler