module Control.Monad.IOSimPOR.Timeout
  ( Timeout
  , timeout
  , unsafeTimeout
  ) where

-- This module provides a timeout function like System.Timeout, BUT
-- garbage collection time is not included (provided GHC stats are
-- enabled, +RTS -T -RTS). Thus this can be used more reliably to
-- limit computation time.

import Control.Concurrent
import Control.Exception (Exception (..), asyncExceptionFromException,
           asyncExceptionToException, bracket, handleJust, uninterruptibleMask_)
import Control.Monad
import Data.Unique (Unique, newUnique)
import GHC.Stats
import System.IO.Unsafe


-- An internal type that is thrown as a dynamic exception to
-- interrupt the running IO computation when the timeout has
-- expired.

-- | An exception thrown to a thread by 'timeout' to interrupt a timed-out
-- computation.

newtype Timeout = Timeout Unique deriving Timeout -> Timeout -> Bool
(Timeout -> Timeout -> Bool)
-> (Timeout -> Timeout -> Bool) -> Eq Timeout
forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
$c== :: Timeout -> Timeout -> Bool
== :: Timeout -> Timeout -> Bool
$c/= :: Timeout -> Timeout -> Bool
/= :: Timeout -> Timeout -> Bool
Eq

-- | @since 4.0
instance Show Timeout where
    show :: Timeout -> String
show Timeout
_ = String
"<<timeout>>"

instance Exception Timeout where
  toException :: Timeout -> SomeException
toException = Timeout -> SomeException
forall e. Exception e => e -> SomeException
asyncExceptionToException
  fromException :: SomeException -> Maybe Timeout
fromException = SomeException -> Maybe Timeout
forall e. Exception e => SomeException -> Maybe e
asyncExceptionFromException

timeout :: Int -> IO a -> IO (Maybe a)
timeout :: forall a. Int -> IO a -> IO (Maybe a)
timeout Int
n IO a
f
    | Int
n Int -> Int -> Bool
forall a. Ord a => a -> a -> Bool
<  Int
0    = (a -> Maybe a) -> IO a -> IO (Maybe a)
forall a b. (a -> b) -> IO a -> IO b
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap a -> Maybe a
forall a. a -> Maybe a
Just IO a
f
    | Int
n Int -> Int -> Bool
forall a. Eq a => a -> a -> Bool
== Int
0    = Maybe a -> IO (Maybe a)
forall a. a -> IO a
forall (m :: * -> *) a. Monad m => a -> m a
return Maybe a
forall a. Maybe a
Nothing
    | Bool
otherwise = do
        pid <- IO ThreadId
myThreadId
        ex  <- fmap Timeout newUnique
        handleJust (\Timeout
e -> if Timeout
e Timeout -> Timeout -> Bool
forall a. Eq a => a -> a -> Bool
== Timeout
ex then () -> Maybe ()
forall a. a -> Maybe a
Just () else Maybe ()
forall a. Maybe a
Nothing)
                   (\()
_ -> Maybe a -> IO (Maybe a)
forall a. a -> IO a
forall (m :: * -> *) a. Monad m => a -> m a
return Maybe a
forall a. Maybe a
Nothing)
                   (bracket (forkIOWithUnmask $ \forall a. IO a -> IO a
unmask ->
                                 IO () -> IO ()
forall a. IO a -> IO a
unmask (IO () -> IO ()) -> IO () -> IO ()
forall a b. (a -> b) -> a -> b
$ Int -> IO ()
waitFor Int
n IO () -> IO () -> IO ()
forall a b. IO a -> IO b -> IO b
forall (m :: * -> *) a b. Monad m => m a -> m b -> m b
>> ThreadId -> Timeout -> IO ()
forall e. Exception e => ThreadId -> e -> IO ()
throwTo ThreadId
pid Timeout
ex)
                            (uninterruptibleMask_ . killThread)
                            (\ThreadId
_ -> (a -> Maybe a) -> IO a -> IO (Maybe a)
forall a b. (a -> b) -> IO a -> IO b
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap a -> Maybe a
forall a. a -> Maybe a
Just IO a
f))

waitFor :: Int -> IO ()
waitFor :: Int -> IO ()
waitFor Int
n = do
  t0 <- IO Int
getGCTime
  threadDelay n
  t1 <- getGCTime
  when (t1 > t0) $
    -- allow some extra time because of GC
    waitFor (t1-t0)

getGCTime :: IO Int
getGCTime :: IO Int
getGCTime = RtsTime -> Int
forall a b. (Integral a, Num b) => a -> b
fromIntegral (RtsTime -> Int) -> (RTSStats -> RtsTime) -> RTSStats -> Int
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (RtsTime -> RtsTime -> RtsTime
forall a. Integral a => a -> a -> a
`div` RtsTime
1000) (RtsTime -> RtsTime)
-> (RTSStats -> RtsTime) -> RTSStats -> RtsTime
forall b c a. (b -> c) -> (a -> b) -> a -> c
. RTSStats -> RtsTime
gc_elapsed_ns (RTSStats -> Int) -> IO RTSStats -> IO Int
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> IO RTSStats
getRTSStats

-- | unsafeTimeout n a forces the evaluation of a, with a time limit of n microseconds.
unsafeTimeout :: Int -> a -> Maybe a
unsafeTimeout :: forall a. Int -> a -> Maybe a
unsafeTimeout Int
n a
a = IO (Maybe a) -> Maybe a
forall a. IO a -> a
unsafePerformIO (IO (Maybe a) -> Maybe a) -> IO (Maybe a) -> Maybe a
forall a b. (a -> b) -> a -> b
$ Int -> IO a -> IO (Maybe a)
forall a. Int -> IO a -> IO (Maybe a)
timeout Int
n (IO a -> IO (Maybe a)) -> IO a -> IO (Maybe a)
forall a b. (a -> b) -> a -> b
$ a -> IO a
forall a. a -> IO a
forall (m :: * -> *) a. Monad m => a -> m a
return (a -> IO a) -> a -> IO a
forall a b. (a -> b) -> a -> b
$! a
a