Jean-Marie Gaillourdet wrote:
This is my previous program with your workaround, it is also attached as TypeRepEqLock.hs
[snip]
Compile and execute:
$ ghc-7.0.3 -threaded -rtsopts TypeRepEqLock.hs <snip> $ while true ; do ./TypeRepEqLock +RTS -N ; done Ok Ok Ok Ok Ok Ok Ok Ok Ok TypeRepEqLock: thread blocked indefinitely in an MVar operation Ok Ok Ok ^C^C
This has nothing to do with Data.Typeable though - it appears to be some interaction between unsaferPerformIO and MVars that I do not understand. The following program occasionally terminates with "thread blocked indefinitely in an MVar operation", too (tested on ghc 7.0.3 and 7.2.1): import Control.Concurrent import Control.Exception import Control.Monad import System.IO.Unsafe main :: IO () main = do -- evaluate lock -- adding this line fixes the problem fin1 <- newEmptyMVar fin2 <- newEmptyMVar forkIO $ ping >>= putMVar fin1 forkIO $ ping >>= putMVar fin2 takeMVar fin1 takeMVar fin2 {-# NOINLINE lock #-} lock :: MVar () lock = unsafePerformIO $ newMVar () ping = do () <- takeMVar lock putMVar lock () Since I don't yet understand why this blocks, I cannot say whether it should work or not. Best regards, Bertram