Suggestion: use an IORef and asynchronous exceptions, see below for
untested code.
On Wed, Dec 21, 2011 at 6:52 AM, Fedor Gogolev
Hello. I'm trying to get some threads that I can stop and get last values that was computed (and that values are IO values, in fact). Here is my first approach:
module Main where
import Control.Concurrent (MVar, threadDelay, forkIO, newMVar, putMVar, readMVar)
tick :: Int -> IO Int tick v = return $ v + 1
loop :: MVar Bool -> a -> (a -> IO a) -> IO a loop var init loopfun = do next <- loopfun init shouldStop <- readMVar var case shouldStop of True -> return next False -> loop var next loopfun
loop :: IORef a -> (a -> IO a) -> IO () loop var loopfun = readIORef var >>= go where go val = do next <- loopfun val writeIORef var next go next
runLoop :: Int -> IO () runLoop timeout = do var <- newMVar False forkIO $ threadDelay timeout >> putMVar var True value <- loop var 0 tick print value
runLoop timeout = do var <- newIORef 0 lock <- newEmptyMVar loopTid <- forkIO $ loop var tick >> putMVar lock () delayTid <- forkIO $ threadDelay timeout >> killThread loopTid >> putMVar lock () takeMVar lock killThread delayTid value <- readIORef var print value
main :: IO () main = runLoop 30000000
The problem is that it looks a little messy and what's worse it leaks memory. So I'm wondering if there is a better approach to do so or some fix to memory leak.
Again, code above is untested and was written on my e-mail client =). But the idea seems fine. Cheers, -- Felipe.