#10737: GHC panic durring MVar operation -------------------------------------+------------------------------------- Reporter: dohaqatar7 | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Windows Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- The following error message was displayed while loading a program into ghci by executing `:r` in a ghci session: {{{ ghc.exe: panic! (the 'impossible' happened) (GHC version 7.8.3 for x86_64-unknown-mingw32): thread blocked indefinitely in an MVar operation Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} The only edit made to the source file before compiling was the removal of an unnecessary `do` on line 20 of the source file. The `do` was used even though the monodic computations were written in a single line style. I have not been able to reproduce the panic at all. The source file, unedited since the panic, now compiles without error. The ghci session leading up to the crash is below {{{ *Main> :t runState (filterM untouchable [1..3]) M.empty runState (filterM untouchable [1..3]) M.empty :: ([Int], M.Map Int Int) *Main> runState (filterM untouchable [1..3]) M.empty ([2],fromList [(1,1),(2,1),(3,1),(4,3)]) *Main> runState (filterM untouchable [1..10]) M.empty ([2,5],fromList [(1,1),(2,1),(3,1),(4,3),(5,1),(6,6),(7,1),(8,7),(9,4),(10,8),(11,1),(12,16),(13,1),(14,10),(15,9),(16,15),(17,1),(18,21),(19,1),(20,22),(21,11),(22,14),(23,1),(24,36),(25,6),(26,16),(27,13),(28,28),(29,1),(30,42),(31,1),(32,31),(33,15),(34,20),(35,13),(36,55),(37,1),(38,22),(39,17),(40,50),(41,1),(42,54),(43,1),(44,40),(45,33),(46,26),(47,1),(48,76),(49,8),(50,43),(51,21),(52,46),(53,1),(54,66),(55,17),(56,64),(57,23),(58,32),(59,1),(60,108),(61,1),(62,34),(63,41),(64,63),(65,19),(66,78),(67,1),(68,58),(69,27),(70,74),(71,1)(72,123),(73,1),(74,40),(75,49),(76,64),(77,19),(78,90),(79,1),(80,106),(81,40)]) *Main> runState (filterM untouchable [1..100]) M.empty ([2,5,52,88Interrupted. *Main> *Main> *Main> *Main> *Main> *Main> *Main> *Main> *Main> :r [1 of 1] Compiling Main ( C:\Users\admin\Programming\Haskell\codegolf\Untouchable.hs, interpreted ) Ok, modules loaded: Main. *Main> ghc.exe: panic! (the 'impossible' happened) (GHC version 7.8.3 for x86_64-unknown-mingw32): thread blocked indefinitely in an MVar operation Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10737 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler