leak.hs

-- stack ghc logger.hs --resolver lts-18.5  -- -O2
-- htop shows 600M leak even when tchans are empty

import Prelude hiding (read)
import Control.Monad
import Control.Concurrent
import Control.Concurrent.STM.TChan
import Control.Concurrent.STM

c :: Int
c = 10000000

write :: TChan String -> IO ()
write ch = do
  replicateM_ c (atomically $ writeTChan ch "string")

read :: TChan String -> IO ()
read ch = replicateM_ c (atomically (readTChan ch))

main :: IO ()
main = do
  (w, r) <- atomically $ do
    w <- newBroadcastTChan
    r <- dupTChan w
    pure (w, r)
  forkIO (threadDelay (10^6) >> read r >> print "Reading done") -- Wait till the queue is full
  write w >> print "Writing done"
  threadDelay (2 * 10^6)
  atomically (isEmptyTChan r) >>= print
  threadDelay (100 * 10^6) -- Prevent exit