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{-# LANGUAGE ScopedTypeVariables #-}
-- !!! test threadDelay, Random, and QSemN.
-- start a large number (n) of threads each of which will wait for a
-- random delay between 0 and m seconds. We use a semaphore to wait
-- for all the threads to finish.
import System.Random
import Control.Concurrent
import Control.Exception
n = 5000 -- no. of threads
m = 3000 -- maximum delay
main = do
s <- newQSemN n
(is :: [Int]) <- sequence (take n (repeat (getStdRandom (randomR (1,m)))))
mapM (fork_sleep s) is
waitQSemN s n
where
fork_sleep s i = forkIO (do waitQSemN s 1
threadDelay (i*1000)
signalQSemN s 1)
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