Stretching the Storage Manager a little too much...

[Simon Marlow]

Michael Weber wrote:
> [I am reading ghc-bugs via the list archives, Cc'ing me would make me 
> see responses faster]
> 
> Here's a simple memoization function:
> 
> applyMemo :: (Eq a1,Show a1) => (a1 -> b) -> MVar [(a1,b)] -> (a1 -> b)
> applyMemo f refTable x1 = unsafePerformIO $ do
>     -- print x1
>     table <- takeMVar refTable
>     let key = x1
>     case lookup key table of
>       Nothing -> do
>         let result = f x1
>         putMVar refTable $! (key,result):table
>         return result
>       Just memo -> putMVar refTable table >> return memo
> 
> 
> The code above is a cut-down example.  Initially, I tried to use 
> Data.HashTable, then IORef (Data.Map ...), then MVars.  However, what 
> remains is that I get funny results: <<loop>>, "thread blocked 
> indefinitely", hangs, depending on the exact implementation of 
> applyMemo, whether I use ghci or ghc, and which function I memoize 
> (something with a more interesting call pattern than fib).

Would you mind submitting a complete test case that we can use to reproduce the 
problem?  We can probably reconstruct one from your description, but you 
probably already have the code lying around.

Cheers,
	Simon