Is this a concurrency bug in base?
haskell3 at davidb.org
Sun Oct 9 19:54:29 CEST 2011
On Sun, Oct 09, 2011 at 03:30:20PM +0200, Jean-Marie Gaillourdet wrote:
>On 09.10.2011, at 14:45, Daniel Fischer wrote:
>> On Sunday 09 October 2011, 13:52:47, Jean-Marie Gaillourdet wrote:
>>> This seems to be a Heisenbug as it is extremely fragile, when adding a
>>> "| grep 1" to the while loop it seems to disappears. At least on my
>> Still produces 1s here with a grep.
>Well, it may have been bad luck on my site.
The program below will occasionally print "1 /= 0" or "0 /= 1" on
x86_64 linux with the Debian testing 7.0.4 ghc.
$ ghc bug -rtsopts -threaded
$ while true; do ./bug +RTS -N; done
> module Main where
> import Control.Monad
> import Control.Concurrent
> import Data.Typeable
> main :: IO ()
> main = do
> fin1 <- newEmptyMVar
> fin2 <- newEmptyMVar
> forkIO $ child fin1
> forkIO $ child fin2
> a <- takeMVar fin1
> b <- takeMVar fin2
> when (a /= b) $
> putStrLn $ show a ++ " /= " ++ show b
> child :: MVar Int -> IO ()
> child var = do
> key <- typeRepKey (typeOf ())
> putMVar var key
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