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|
{- thread scheduling
-
- Copyright 2012 Joey Hess <joey@kitenet.net>
- Copyright 2011 Bas van Dijk & Roel van Dijk
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Utility.ThreadScheduler where
import Common
import Control.Concurrent
import Control.Exception
import Control.Concurrent.Async
import System.Posix.Terminal
import System.Posix.Signals
newtype Seconds = Seconds { fromSeconds :: Int }
deriving (Eq, Ord, Show)
{- Runs an action repeatedly forever, sleeping at least the specified number
- of seconds in between. -}
runEvery :: Seconds -> IO a -> IO a
runEvery n a = forever $ do
threadDelaySeconds n
a
threadDelaySeconds :: Seconds -> IO ()
threadDelaySeconds (Seconds n) = unboundDelay (fromIntegral n * oneSecond)
where
oneSecond = 1000000 -- microseconds
{- Like threadDelay, but not bounded by an Int.
-
- There is no guarantee that the thread will be rescheduled promptly when the
- delay has expired, but the thread will never continue to run earlier than
- specified.
-
- Taken from the unbounded-delay package to avoid a dependency for 4 lines
- of code.
-}
unboundDelay :: Integer -> IO ()
unboundDelay time = do
let maxWait = min time $ toInteger (maxBound :: Int)
threadDelay $ fromInteger maxWait
when (maxWait /= time) $ unboundDelay (time - maxWait)
{- Runs an action until a timeout is reached. If it fails to complete in
- time, or throws an exception, returns a Left value.
-
- Note that if the action runs an unsafe foreign call, the signal to
- cancel it may not arrive until the call returns. -}
runTimeout :: Seconds -> IO a -> IO (Either SomeException a)
runTimeout secs a = do
runner <- async a
controller <- async $ do
threadDelaySeconds secs
cancel runner
cancel controller `after` waitCatch runner
{- Pauses the main thread, letting children run until program termination. -}
waitForTermination :: IO ()
waitForTermination = do
lock <- newEmptyMVar
check softwareTermination lock
whenM (queryTerminal stdInput) $
check keyboardSignal lock
takeMVar lock
where
check sig lock = void $
installHandler sig (CatchOnce $ putMVar lock ()) Nothing
|
