[GHC] #10639: Optimization changes concurrent program's behaviour

14 Jul 2015

      #10639: Optimization changes concurrent program's behaviour
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              Reporter:  gizmo.mk0   |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.10.1
              Keywords:              |  Operating System:  Windows
          Architecture:  x86_64      |   Type of failure:  Incorrect result
  (amd64)                            |  at runtime
             Test Case:              |        Blocked By:
              Blocking:              |   Related Tickets:
Differential Revisions:              |
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 Here is a program that spawns a thread from the main thread, which tries
 to constantly write out a message to the console.

 {{{#!hs
 module Main where

 import Control.Concurrent (forkIO)

 main :: IO ()
 main = do
   _ <- forkIO $ runForever $ putStrLn "Hey"
   runForever $ return ()

 runForever :: IO () -> IO ()
 runForever action = action >> runForever action
 }}}

 If you compile it with 'ghc main', it works correctly - it prints out the
 message continuously, and you can terminate it by pressing Ctrl-C.
 However, if you compile it with 'ghc -O main' (or -O2, or -O3...), it
 doesn't print out anything, and the only way to exit is to kill the
 process from Task Manager.

 This was reproducable with GHC 7.10.1, on a Windows 7 x64 machine, with an
 AMD A4-5300 APU.

 ''(Disclaimer: this is my first bugreport, and I'm not sure what else can
 I do to investigate this issue.)''

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10639
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