On 12/10/2011 12:24, Bertram Felgenhauer wrote:
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.
I think it should work. Could you make a ticket for it please? Cheers, Simon