bug in dupChan

[Meurig Sage]

Hi 
I think that there's a bug in dupChan in Chan.lhs

I tried the following program. 

main = do
 chan <- newChan
 ch <- dupChan chan
 writeChan chan "done"
 x <- readChan chan
 y <- readChan ch
 prnt ("Got "++x ++" "++y)

Now if I remember correctly this should print "Got done done".

Instead it exits with 
C:\Test\test.exe: no threads to run:  infinite loop or deadlock?

I looked for the code for dupChan in hslibs and it says

dupChan :: Chan a -> IO (Chan a)
dupChan (Chan _read write) = do
   new_read <- newEmptyMVar
   hole     <- readMVar write
   putMVar new_read hole
   return (Chan new_read write)

Shouldn't this instead be 

dupChan :: Chan a -> IO (Chan a)
dupChan (Chan _read write) = do
   new_read <- newEmptyMVar
   hole     <- readMVar write
   putMVar new_read hole
** putMVar write hole **
   return (Chan new_read write)

That's at least what the Concurrent haskell paper says.

Hugs 98 seems to have the same bug with its library.

Meurig
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.haskell.org/pipermail/glasgow-haskell-bugs/attachments/20010124/715467fe/attachment.htm