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module Control.Concurrent.Delay where
import Control.Concurrent
import Control.Monad
import Control.Exception ({-evaluate,-}handle,finally,throwIO)
import Data.Time.Clock (NominalDiffTime)
import System.IO.Error
type Microseconds = Int
microseconds :: NominalDiffTime -> Microseconds
microseconds d = round $ 1000000 * d
data InterruptibleDelay = InterruptibleDelay
{ delayThread :: MVar ThreadId
}
interruptibleDelay :: IO InterruptibleDelay
interruptibleDelay = do
fmap InterruptibleDelay newEmptyMVar
-- | Delay for the given number of microseconds and return 'True' if the delay
-- is not interrupted.
--
-- Note: If a thread is already waiting on the given 'InterruptibleDelay'
-- object, then this will block until it becomes available and only then start
-- the delay timer.
startDelay :: InterruptibleDelay -> Microseconds -> IO Bool
startDelay d interval = do
thread <- myThreadId
handle (\e -> do when (not $ isUserError e) (throwIO e)
return False) $ do
putMVar (delayThread d) thread
threadDelay interval
void $ takeMVar (delayThread d)
return True
-- The following cleanup shouldn't be necessary, but I'm paranoid.
`finally` tryTakeMVar (delayThread d)
where debugNoise str = return ()
-- | Signal the thread waiting on the given 'InterruptibleDelay' object to
-- continue even though the timeout has not elapsed. If no thread is waiting,
-- then this is a no-op.
interruptDelay :: InterruptibleDelay -> IO ()
interruptDelay d = do
mthread <- tryTakeMVar (delayThread d)
forM_ mthread $ \thread -> do
throwTo thread (userError "Interrupted delay")
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