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

Here's a "fun" one:

*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.:

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.

Trac metadata

Trac field	Value
Version	7.10.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	low
Resolution	Unresolved
Component	GHCi
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