[GHC] #11771: ghc.exe: `panic'! (the 'impossible' happened); thread blocked indefinitely in an MVar operation

29 Mar 2016

      #11771: ghc.exe: `panic'! (the 'impossible' happened); thread blocked indefinitely
in an MVar operation
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           Reporter:  YoYoYonnY         |             Owner:
               Type:  bug               |            Status:  new
           Priority:  low               |         Milestone:
          Component:  GHCi              |           Version:  7.10.3
           Keywords:                    |  Operating System:  Windows
       Architecture:  Unknown/Multiple  |   Type of failure:  GHCi crash
          Test Case:                    |        Blocked By:
           Blocking:                    |   Related Tickets:
Differential Rev(s):                    |         Wiki Page:
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 Here's a "fun" one:

 {{{#!hs
 *Main> main
 Interrupted.
 *Main>
 *Main> !cl
 ghc.exe: panic! (the 'impossible' happened)
   (GHC version 7.10.3 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
...
ghci --version
The Glorious Glasgow Haskell Compilation System, version 7.10.3
 }}}

 Don't mind the {{{!cl}}}, GHC crashed as soon as the interupt was
 registered, I usually {{{:!cls}}} after I execute main.

 I will backup the code in case someone wants to see if it's a bug in my
 program, but I didn't use multithreading myself, and I don't think the
 vector, unordered-containers, bytestring and parsec packages use threading
 either (all heavily at work, though)...

 The interupt was nececairy because my code was generating a infinite
 (oops) collection of these bad boys, using all sorts of folds, maps, etc.:
 {{{#!hs
 newtype ParserData = ParserData
     { unpackParserData :: HashMap
         ByteString
         (ParserData -> Either ByteString (Parser ())) }
 }}}

 I am wondering if this could be a problem with Windows, because the system
 was running slow at the time of the interupt; The {{{Alt+Tab}}} screen
 didn't appear until after the interupt.

 I don't think I can manage to reproduce this bug, which is unfortunate
 aswell (low priority because of that :c).

 Either way, it crashed, that's all I can tell you for sure.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11771
GHC http://www.haskell.org/ghc/
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