Difference between revisions of "Simple STM example"

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<haskell>
  
<haskell>
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{-# OPTIONS_GHC -rtsopts -with-rtsopts=-N4 -threaded -Wall #-}
 
module Main where
  
module Main where
 
import Control.Monad
  
import Control.Monad
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import Control.Concurrent.STM
  
import Control.Concurrent.STM
   
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main :: IO ()
−
main = do shared <- atomically $ newTVar 0
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main = do shared <- newTVarIO (0 :: Int)
 
before <- atomRead shared
  
before <- atomRead shared
−
putStrLn $ "Before: " ++ show before
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putStrLn ("Before: " ++ show before)
−
forkIO $ 25 `timesDo` (dispVar shared >> milliSleep 20)
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repeatIO 25 (dispVar shared >> threadDelay 20_000)
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forkIO $ 10 `timesDo` (appV ((+) 2) shared >> milliSleep 50)
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repeatIO 10 (appV (+ 2) shared >> threadDelay 50_000)
−
forkIO $ 20 `timesDo` (appV pred shared >> milliSleep 25)
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repeatIO 20 (appV pred shared >> threadDelay 25_000)
−
milliSleep 800
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threadDelay 800_000
 
after <- atomRead shared
  
after <- atomRead shared
−
putStrLn $ "After: " ++ show after
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putStrLn ("After: " ++ show after)
  +
where
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where timesDo = replicateM_
  
−
milliSleep = threadDelay . (*) 1000
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repeatIO n = void . forkIO . replicateM_ n
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atomRead = readTVarIO
−  
  ⚫
dispVar x = atomRead x >>= print
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atomRead = atomically . readTVar
  
  ⚫
appV fn x = atomically (modifyTVar x fn)
⚫
dispVar x = atomRead x >>= print
  
⚫
appV fn x = atomically $ readTVar x >>= writeTVar x . fn
  
 
</haskell>
  
</haskell>
 
[[Category:Monad]]
  
[[Category:Monad]]
  +
[[Category:Code]]

Latest revision as of 09:01, 9 September 2024

{-# OPTIONS_GHC -rtsopts -with-rtsopts=-N4 -threaded -Wall #-}
module Main where
import Control.Monad
import Control.Concurrent
import Control.Concurrent.STM

main :: IO ()
main = do shared <- newTVarIO (0 :: Int)
          before <- atomRead shared
          putStrLn ("Before: " ++ show before)
          repeatIO 25 (dispVar shared >> threadDelay 20_000)
          repeatIO 10 (appV (+ 2) shared >> threadDelay 50_000)
          repeatIO 20 (appV pred shared >> threadDelay 25_000)
          threadDelay 800_000
          after <- atomRead shared
          putStrLn ("After: " ++ show after)
  where
    repeatIO n = void . forkIO . replicateM_ n
    atomRead = readTVarIO
    dispVar x = atomRead x >>= print
    appV fn x = atomically (modifyTVar x fn)
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