Fair concurrent `map` function in haskell?

Question

Say I am simulating a network of some sort, and have a function which broadcasts a value over a list of Chans:

broadcast :: a -> [Receiver] -> IO ()
broadcast a = mapM_ (send a)

This will "send" the data to each Receiver in order. I would like instead to broadcast nondeterministically to all of the Receivers.

Thanks for any clues.

score 3 · Answer 1 · answered May 10 '11 at 05:15

3

How about just using GHC's concurrency?

broadcast :: a -> [Receiver] -> IO ()
broadcast a = mapM_ (forkIO . send a)

Then make sure to use the threaded RTS (compile with ghc -threaded).

answered May 10 '11 at 05:15

1

That introduces some nondeterminism, sure, and for certain applications I can see it being the right way. But I'd suspect that the order in which messages are received, while nondeterministic, would generally stick pretty close to a linear ordering. If you want to ensure that things are mixed up, better to do so explicitly. – sclv May 10 '11 at 05:52
Perhaps also introduce a random delay after forking off each thread? Your solution makes sense for this restricted scenario, but I suspect that once you introduce any complications like communication, it won't generalise. – Ganesh Sittampalam May 10 '11 at 06:28

score 2 · Answer 2 · answered May 09 '11 at 22:47

2

broadcast a rs = do 
   g <- newStdGen
   mapM_ (send a) $ shuffle' rs (length rs) g

answered May 09 '11 at 22:47

sclv

2 Answers2