#14356: "Main: thread blocked indefinitely in an MVar operation" in fixIO -------------------------------------+------------------------------------- Reporter: nickkuk | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Runtime System | Version: 8.2.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Old description:
I'm not sure whether such behavior is expected, but this program {{{ import System.IO
main = fixIO (\x -> return 1) >>= print }}} prints "1"; and this {{{ import System.IO
main = fixIO (\(x, _) -> return (1, print x)) >>= print . fst }}} prints "Main: thread blocked indefinitely in an MVar operation".
Second program arises from something like {{{ {-# LANUGAGE RecursiveDo #-}
main = mdo ... x <- return 1 let f = do ... print x ... ... return f }}} It is not necessary to call f somewhere in mdo to get "Main: thread blocked indefinitely in an MVar operation".
New description: I'm not sure whether such behavior is expected, but this program {{{#!hs import System.IO main = fixIO (\x -> return 1) >>= print }}} prints "1"; and this {{{#!hs import System.IO main = fixIO (\(x, _) -> return (1, print x)) >>= print . fst }}} prints "Main: thread blocked indefinitely in an MVar operation". Second program arises from something like {{{#!hs {-# LANUGAGE RecursiveDo #-} main = mdo ... x <- return 1 let f = do ... print x ... ... return f }}} It is not necessary to call f somewhere in mdo to get "Main: thread blocked indefinitely in an MVar operation". -- Comment (by bgamari): David, could you look at this? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14356#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler