Commit 50d6631d authored by Yuanle Song's avatar Yuanle Song
Browse files

add try4.hs on STM

parent 005e98d3

queue-base-threading.cabal

+7 −0
Original line number Diff line number Diff line
@@ -49,6 +49,13 @@ executable testQueue 
                     , random

  default-language:    Haskell2010



executable try4

  main-is:             try4.hs

  ghc-options:         -threaded -rtsopts -with-rtsopts=-N

  build-depends:       base

                     , random

                     , stm

  default-language:    Haskell2010



source-repository head

  type:     git

try1.hs

+1 −0
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@@ -24,3 +24,4 @@ main = do 
  counter <- newMVar 0

  replicateM_ 10 (forkIO $ incrementAndPrint counter)

  putStrLn "Finishing up"

  threadDelay 1000000

try4.hs

0 → 100644
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Original line number Diff line number Diff line 
-- can I write this using STM? I know the print part is not pure function.

-- STM can help with variable read/write, but it can't help you with IO

-- action.  since there is really no variable in haskell, it's similar to try1

-- where it is implemented using locks (MVar). STM TVar is implemented using

-- transactional memory. STM can only ensure TVar and T* access is safe in

-- atomically block, it can't do anything about printing.



import System.IO

import Control.Concurrent

import Control.Concurrent.STM

import Text.Printf

import System.Random



fuzz :: IO ()

fuzz = do

  seconds <- (getStdRandom random :: IO Double)

  threadDelay $ round (realToFrac (1000 * seconds))



incrementAndPrint :: TVar Integer -> IO ()

incrementAndPrint counter = do

  fuzz

  newCount <- atomically $ do

    modifyTVar' counter (\i -> i + 1)

    readTVar counter

  fuzz

  printf "The count is %d\n" newCount

  fuzz

  putStrLn "---------------"



main :: IO ()

main = do

  putStrLn "Starting up"

  counter <- newTVarIO 0

  replicateM_ 10 (forkIO $ incrementAndPrint counter)

  putStrLn "Finishing up"