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
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