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{-# LANGUAGE BangPatterns #-}
module Main where
import qualified Data.ByteString as S
import Data.IORef
import Control.Monad
makeBs :: Int -> S.ByteString
makeBs n = S.replicate n (fromIntegral n)
doStuff :: IORef [S.ByteString] -> Int -> IO ()
doStuff ref n = do
let !bs = makeBs n
modifyIORef ref (bs:)
{-# NOINLINE doStuff #-}
undo :: IORef [S.ByteString] -> IO ()
undo ref = do
h <- atomicModifyIORef ref (\(x:xs) -> (xs,x))
S.length h `seq` return ()
main = do
ref <- newIORef [S.empty]
let fn n = do
doStuff ref n
when (rem 5 n /= 0 ) $ undo ref
mapM_ fn (take 5000000 $ cycle [1..100])
var <- readIORef ref
print $ length var
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