[GHC] #10737: GHC panic durring MVar operation

[GHC]

#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:              |
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 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>
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