On Sun, Oct 09, 2011 at 03:30:20PM +0200, Jean-Marie Gaillourdet wrote:
Hi Daniel,
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 computers.
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