[GHC] #11175: Holding Ctrl+C on Windows GHCI Prompt crashes with concurrency panic

[GHC]

#11175: Holding Ctrl+C on Windows GHCI Prompt crashes with concurrency panic
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           Reporter:  cwfenner          |             Owner:
               Type:  bug               |            Status:  new
           Priority:  lowest            |         Milestone:
          Component:  GHCi              |           Version:  7.10.2
           Keywords:                    |  Operating System:  Windows
       Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
          Test Case:                    |        Blocked By:
           Blocking:                    |   Related Tickets:
Differential Rev(s):                    |         Wiki Page:
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 When I hold Control-C in the GHCI prompt (on either Windows Powershell or
 Command Prompt), then release, the prompt stops responding. The first few
 keystrokes will be ignored altogether, then the next ignored
 intermittently.

 After typing around 5 words, GHCi crashes with the following output:

 {{{
 ghc.exe: panic! (the 'impossible' happened)
   (GHC version 7.10.2 for x86_64-unknown-mingw32):
         thread blocked indefinitely in an MVar operation
 }}}

 If I don't type after holding Ctrl+C, GHCi seems to sit happily without
 crashing. No amount of waiting after holding Ctrl+C seems to make it
 recover. It does not matter whether I press return or not.

 However, faster typing seems to make it crash in fewer keystrokes.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11175>
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