Is this a concurrency bug in base?

[Jean-Marie Gaillourdet]

Hi,

the Eq instance of TypeRep shows the same non-deterministic behavior:

import Control.Concurrent
import Control.Exception
import Control.Monad
import Data.Typeable

main :: IO ()
main =
 do { fin1 <- newEmptyMVar
    ; fin2 <- newEmptyMVar

    ; forkIO $ return (typeOf ()) >>= evaluate >>= putMVar fin1 
    ; forkIO $ return (typeOf ()) >>= evaluate >>= putMVar fin2 
    
    ; t1 <- takeMVar fin1
    ; t2 <- takeMVar fin2
    ; when (t1 /= t2) $
        putStrLn $ "typeOf " ++ show t1 ++ " /= typeOf " ++ show t2
    }

$ ghc-7.0.3 -threaded -rtsopts TypeRepEq.hs
<snip>
$ while true ; do ./TypeRepEq +RTS -N ; done
typeOf () /= typeOf ()
typeOf () /= typeOf ()
^C^C

$

On 09.10.2011, at 16:04, David Brown wrote:
> 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

Thanks again for reproducing it.

Jean