RFC: termination detection for STM

[Simon Marlow]

Michael Stahl wrote:

> here is the simplest thing i could come up with that has threads which are
> blocked indefinitely but not gc'd.
> 

This example isn't deadlocked: it just waits 10 seconds and then receives the 
BlockedIndefinitely exception.  Can you construct an example that has a real 
deadlock that isn't detected?

Cheers,
	Simon

> 
> module Main where
> import Control.Monad.STM
> import Control.Concurrent.STM.TVar
> import Control.Concurrent.STM.TChan
> import Control.Concurrent
> 
> type Store' = TChan (TVar Int)
> 
> main = do
>         (store,store') <- atomically $ do
>                 c <- newTChan
>                 c' <- dupTChan c
>                 v <- newTVar 0
>                 writeTChan c v
>                 return (c,c')
>         forkIO $ rule store
>         threadDelay 10000000 -- wait for termination
>         print' store'
>    where
>         rule store = do
>                 x <- atomically $
>                         readTChan store
>                 forkIO $ match x
>                 rule store
>         match x = do
>                 atomically $ do
>                         readTVar x
>                         retry
>         print' store = do
>                 x <- atomically $ do
>                         v <- readTChan store
>                         readTVar v
>                 print x
>                 print' store