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module Main where
import Control.Concurrent
import Control.Monad
main = do
m <- newEmptyMVar
done <- newEmptyMVar
let q = 200000
forkIO (do mapM (\n -> putMVar m n) [1..q]; putMVar done ())
forkIO (do replicateM_ q $ readMVar m; putMVar done ())
forkIO (do replicateM_ q $ tryReadMVar m; putMVar done ())
forkIO (do replicateM_ q $ takeMVar m; putMVar done ())
replicateM_ 4 $ takeMVar done
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