[Haskell-cafe] Race Condition in threads
Hello All I have two questions. 1. I wrote this code to create 10 simultaneous threads. Could some one please tell me if this is correct or not ? incr_count :: MVar () - MVar Int - IO () incr_count m n = ( forM_ [ 1..1 ] $ \_ - modifyMVar_ n ( return . ( + 10 ) ) ) putMVar m () main :: IO() main = do count - newMVar 0 list - forM [1..10] $ \_ - newEmptyMVar forM_ list $ \var - forkIO . incr_count var $ count forM_ list $ \var - takeMVar var val - takeMVar count print val 2. I am trying to create race condition which makes the variable in inconsistent state. Could some one please tell me how to achieve this ? I look at IORef but it does not have function like modifyMVar_. Mukesh Tiwari ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Race Condition in threads
2012/12/18 mukesh tiwari mukeshtiwari.ii...@gmail.com: Hello All I have two questions. 1. I wrote this code to create 10 simultaneous threads. Could some one please tell me if this is correct or not ? incr_count :: MVar () - MVar Int - IO () incr_count m n = ( forM_ [ 1..1 ] $ \_ - modifyMVar_ n ( return . ( + 10 ) ) ) putMVar m () main :: IO() main = do count - newMVar 0 list - forM [1..10] $ \_ - newEmptyMVar forM_ list $ \var - forkIO . incr_count var $ count forM_ list $ \var - takeMVar var val - takeMVar count print val It is pretty much correct (some comments would be nice, though). 2. I am trying to create race condition which makes the variable in inconsistent state. Could some one please tell me how to achieve this ? I look at IORef but it does not have function like modifyMVar_. MVars are atomic in the sense that they have empty state and mutator can wait until variable will have a value. So you have to operate with something else, either IORef or with readMVar instead of takeMVar or modifyMVar_. Mukesh Tiwari ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Race Condition in threads
Hi Serguey Thank you for reply. I tried with IORef but I am missing a function which modify it. In this case every thread just write value 10 to variable n. incr_count :: MVar () - IORef Int - IO () incr_count m n = ( forM_ [ 1 .. 1 ] $ \_ - writeIORef n 10 ) putMVar m () main :: IO () main = do count - newIORef 0 list - forM [1..10] $ \_ - newEmptyMVar forM_ list $ \var - forkIO . incr_count var $ count forM_ list $ \var - takeMVar var val - readIORef count print val ghci:t atomicModifyIORef atomicModifyIORef :: IORef a - (a - (a, b)) - IO b ghci:t readIORef readIORef :: IORef a - IO a ghci:t writeIORef writeIORef :: IORef a - a - IO () I have atomicModifyIORef but it puts it into IO. I am missing some thing like this ghci:t modifyMVar_ modifyMVar_ :: MVar a - (a - IO a) - IO () modifyIORef_:: IORef a - ( a - IO a ) - IO () Mukesh Tiwari On Tue, Dec 18, 2012 at 11:50 PM, Serguey Zefirov sergu...@gmail.comwrote: 2012/12/18 mukesh tiwari mukeshtiwari.ii...@gmail.com: Hello All I have two questions. 1. I wrote this code to create 10 simultaneous threads. Could some one please tell me if this is correct or not ? incr_count :: MVar () - MVar Int - IO () incr_count m n = ( forM_ [ 1..1 ] $ \_ - modifyMVar_ n ( return . ( + 10 ) ) ) putMVar m () main :: IO() main = do count - newMVar 0 list - forM [1..10] $ \_ - newEmptyMVar forM_ list $ \var - forkIO . incr_count var $ count forM_ list $ \var - takeMVar var val - takeMVar count print val It is pretty much correct (some comments would be nice, though). 2. I am trying to create race condition which makes the variable in inconsistent state. Could some one please tell me how to achieve this ? I look at IORef but it does not have function like modifyMVar_. MVars are atomic in the sense that they have empty state and mutator can wait until variable will have a value. So you have to operate with something else, either IORef or with readMVar instead of takeMVar or modifyMVar_. Mukesh Tiwari ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
