GHC/Event/Thread.hs

{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE BangPatterns, NoImplicitPrelude #-}
module GHC.Event.Thread
 ( getSystemEventManager
 , getSystemTimerManager
 , ensureIOManagerIsRunning
 , ioManagerCapabilitiesChanged
 , threadWaitRead
 , threadWaitWrite
 , threadWaitReadSTM
 , threadWaitWriteSTM
 , closeFdWith
 , threadDelay
 , registerDelay
 ) where

import Control.Exception (finally)
import Control.Monad (forM, forM_, sequence_, zipWithM, when)
import Data.IORef (IORef, newIORef, readIORef, writeIORef)
import Data.List (zipWith3)
import Data.Maybe (Maybe(..))
import Data.Tuple (snd)
import Foreign.C.Error (eBADF, errnoToIOError)
import Foreign.Ptr (Ptr)
import GHC.Base
import GHC.Conc.Sync (TVar, ThreadId, ThreadStatus(..), atomically, forkIO,
 labelThread, modifyMVar_, withMVar, newTVar, sharedCAF,
 getNumCapabilities, threadCapability, myThreadId, forkOn,
 threadStatus, writeTVar, newTVarIO, readTVar, retry,throwSTM,STM)
import GHC.IO (mask_, onException)
import GHC.IO.Exception (ioError)
import GHC.IOArray (IOArray, newIOArray, readIOArray, writeIOArray,
 boundsIOArray)
import GHC.MVar (MVar, newEmptyMVar, newMVar, putMVar, takeMVar)
import GHC.Event.Internal (eventIs, evtClose)
import GHC.Event.Manager (Event, EventManager, evtRead, evtWrite, loop,
 new, registerFd, unregisterFd_)
import qualified GHC.Event.Manager as M
import qualified GHC.Event.TimerManager as TM
import GHC.Num ((-), (+))
import System.IO.Unsafe (unsafePerformIO)
import System.Posix.Types (Fd)

-- | Suspends the current thread for a given number of microseconds
-- (GHC only).
--
-- 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.
threadDelay :: Int -> IO ()
threadDelay usecs = mask_ $ do
 mgr <- getSystemTimerManager
 m <- newEmptyMVar
 reg <- TM.registerTimeout mgr usecs (putMVar m ())
 takeMVar m `onException` TM.unregisterTimeout mgr reg

-- | Set the value of returned TVar to True after a given number of
-- microseconds. The caveats associated with threadDelay also apply.
--
registerDelay :: Int -> IO (TVar Bool)
registerDelay usecs = do
 t <- atomically $ newTVar False
 mgr <- getSystemTimerManager
 _ <- TM.registerTimeout mgr usecs . atomically $ writeTVar t True
 return t

-- | Block the current thread until data is available to read from the
-- given file descriptor.
--
-- This will throw an 'IOError' if the file descriptor was closed
-- while this thread was blocked. To safely close a file descriptor
-- that has been used with 'threadWaitRead', use 'closeFdWith'.
threadWaitRead :: Fd -> IO ()
threadWaitRead = threadWait evtRead
{-# INLINE threadWaitRead #-}

-- | Block the current thread until the given file descriptor can
-- accept data to write.
--
-- This will throw an 'IOError' if the file descriptor was closed
-- while this thread was blocked. To safely close a file descriptor
-- that has been used with 'threadWaitWrite', use 'closeFdWith'.
threadWaitWrite :: Fd -> IO ()
threadWaitWrite = threadWait evtWrite
{-# INLINE threadWaitWrite #-}

-- | Close a file descriptor in a concurrency-safe way.
--
-- Any threads that are blocked on the file descriptor via
-- 'threadWaitRead' or 'threadWaitWrite' will be unblocked by having
-- IO exceptions thrown.
closeFdWith :: (Fd -> IO ()) -- ^ Action that performs the close.
 -> Fd -- ^ File descriptor to close.
 -> IO ()
closeFdWith close fd = do
 eventManagerArray <- readIORef eventManager
 let (low, high) = boundsIOArray eventManagerArray
 mgrs <- forM [low..high] $ \i -> do
 Just (_,!mgr) <- readIOArray eventManagerArray i
 return mgr
 mask_ $ do
 tables <- forM mgrs $ \mgr -> takeMVar $ M.callbackTableVar mgr fd
 cbApps <- zipWithM (\mgr table -> M.closeFd_ mgr table fd) mgrs tables
 close fd `finally` sequence_ (zipWith3 finish mgrs tables cbApps)
 where
 finish mgr table cbApp = putMVar (M.callbackTableVar mgr fd) table >> cbApp

threadWait :: Event -> Fd -> IO ()
threadWait evt fd = mask_ $ do
 m <- newEmptyMVar
 mgr <- getSystemEventManager_
 reg <- registerFd mgr (\_ e -> putMVar m e) fd evt
 evt' <- takeMVar m `onException` unregisterFd_ mgr reg
 if evt' `eventIs` evtClose
 then ioError $ errnoToIOError "threadWait" eBADF Nothing Nothing
 else return ()


threadWaitSTM :: Event -> Fd -> IO (STM (), IO ())
threadWaitSTM evt fd = mask_ $ do
 m <- newTVarIO Nothing
 mgr <- getSystemEventManager_
 reg <- registerFd mgr (\_ e -> atomically (writeTVar m (Just e))) fd evt
 let waitAction =
 do mevt <- readTVar m
 case mevt of
 Nothing -> retry
 Just evt' ->
 if evt' `eventIs` evtClose
 then throwSTM $ errnoToIOError "threadWaitSTM" eBADF Nothing Nothing
 else return ()
 return (waitAction, unregisterFd_ mgr reg >> return ())

-- | Allows a thread to use an STM action to wait for a file descriptor to be readable.
-- The STM action will retry until the file descriptor has data ready.
-- The second element of the return value pair is an IO action that can be used
-- to deregister interest in the file descriptor.
--
-- The STM action will throw an 'IOError' if the file descriptor was closed
-- while the STM action is being executed. To safely close a file descriptor
-- that has been used with 'threadWaitReadSTM', use 'closeFdWith'.
threadWaitReadSTM :: Fd -> IO (STM (), IO ())
threadWaitReadSTM = threadWaitSTM evtRead
{-# INLINE threadWaitReadSTM #-}

-- | Allows a thread to use an STM action to wait until a file descriptor can accept a write.
-- The STM action will retry while the file until the given file descriptor can accept a write.
-- The second element of the return value pair is an IO action that can be used to deregister
-- interest in the file descriptor.
--
-- The STM action will throw an 'IOError' if the file descriptor was closed
-- while the STM action is being executed. To safely close a file descriptor
-- that has been used with 'threadWaitWriteSTM', use 'closeFdWith'.
threadWaitWriteSTM :: Fd -> IO (STM (), IO ())
threadWaitWriteSTM = threadWaitSTM evtWrite
{-# INLINE threadWaitWriteSTM #-}


-- | Retrieve the system event manager for the capability on which the
-- calling thread is running.
--
-- This function always returns 'Just' the current thread's event manager
-- when using the threaded RTS and 'Nothing' otherwise.
getSystemEventManager :: IO (Maybe EventManager)
getSystemEventManager = do
 t <- myThreadId
 (cap, _) <- threadCapability t
 eventManagerArray <- readIORef eventManager
 mmgr <- readIOArray eventManagerArray cap
 return $ fmap snd mmgr

getSystemEventManager_ :: IO EventManager
getSystemEventManager_ = do
 Just mgr <- getSystemEventManager
 return mgr
{-# INLINE getSystemEventManager_ #-}

foreign import ccall unsafe "getOrSetSystemEventThreadEventManagerStore"
 getOrSetSystemEventThreadEventManagerStore :: Ptr a -> IO (Ptr a)

eventManager :: IORef (IOArray Int (Maybe (ThreadId, EventManager)))
eventManager = unsafePerformIO $ do
 numCaps <- getNumCapabilities
 eventManagerArray <- newIOArray (0, numCaps - 1) Nothing
 em <- newIORef eventManagerArray
 sharedCAF em getOrSetSystemEventThreadEventManagerStore
{-# NOINLINE eventManager #-}

numEnabledEventManagers :: IORef Int
numEnabledEventManagers = unsafePerformIO $ do
 newIORef 0
{-# NOINLINE numEnabledEventManagers #-}

foreign import ccall unsafe "getOrSetSystemEventThreadIOManagerThreadStore"
 getOrSetSystemEventThreadIOManagerThreadStore :: Ptr a -> IO (Ptr a)

-- | The ioManagerLock protects the 'eventManager' value:
-- Only one thread at a time can start or shutdown event managers.
{-# NOINLINE ioManagerLock #-}
ioManagerLock :: MVar ()
ioManagerLock = unsafePerformIO $ do
 m <- newMVar ()
 sharedCAF m getOrSetSystemEventThreadIOManagerThreadStore

getSystemTimerManager :: IO TM.TimerManager
getSystemTimerManager = do
 Just mgr <- readIORef timerManager
 return mgr

foreign import ccall unsafe "getOrSetSystemTimerThreadEventManagerStore"
 getOrSetSystemTimerThreadEventManagerStore :: Ptr a -> IO (Ptr a)

timerManager :: IORef (Maybe TM.TimerManager)
timerManager = unsafePerformIO $ do
 em <- newIORef Nothing
 sharedCAF em getOrSetSystemTimerThreadEventManagerStore
{-# NOINLINE timerManager #-}

foreign import ccall unsafe "getOrSetSystemTimerThreadIOManagerThreadStore"
 getOrSetSystemTimerThreadIOManagerThreadStore :: Ptr a -> IO (Ptr a)

{-# NOINLINE timerManagerThreadVar #-}
timerManagerThreadVar :: MVar (Maybe ThreadId)
timerManagerThreadVar = unsafePerformIO $ do
 m <- newMVar Nothing
 sharedCAF m getOrSetSystemTimerThreadIOManagerThreadStore

ensureIOManagerIsRunning :: IO ()
ensureIOManagerIsRunning
 | not threaded = return ()
 | otherwise = do
 startIOManagerThreads
 startTimerManagerThread

startIOManagerThreads :: IO ()
startIOManagerThreads =
 withMVar ioManagerLock $ \_ -> do
 eventManagerArray <- readIORef eventManager
 let (_, high) = boundsIOArray eventManagerArray
 forM_ [0..high] (startIOManagerThread eventManagerArray)
 writeIORef numEnabledEventManagers (high+1)

restartPollLoop :: EventManager -> Int -> IO ThreadId
restartPollLoop mgr i = do
 M.release mgr
 !t <- forkOn i $ loop mgr
 labelThread t "IOManager"
 return t

startIOManagerThread :: IOArray Int (Maybe (ThreadId, EventManager))
 -> Int
 -> IO ()
startIOManagerThread eventManagerArray i = do
 let create = do
 !mgr <- new True
 !t <- forkOn i $ loop mgr
 labelThread t "IOManager"
 writeIOArray eventManagerArray i (Just (t,mgr))
 old <- readIOArray eventManagerArray i
 case old of
 Nothing -> create
 Just (t,em) -> do
 s <- threadStatus t
 case s of
 ThreadFinished -> create
 ThreadDied -> do
 -- Sanity check: if the thread has died, there is a chance
 -- that event manager is still alive. This could happend during
 -- the fork, for example. In this case we should clean up
 -- open pipes and everything else related to the event manager.
 -- See #4449
 M.cleanup em
 create
 _other -> return ()

startTimerManagerThread :: IO ()
startTimerManagerThread = modifyMVar_ timerManagerThreadVar $ \old -> do
 let create = do
 !mgr <- TM.new
 writeIORef timerManager $ Just mgr
 !t <- forkIO $ TM.loop mgr `finally` shutdownManagers
 labelThread t "TimerManager"
 return $ Just t
 case old of
 Nothing -> create
 st@(Just t) -> do
 s <- threadStatus t
 case s of
 ThreadFinished -> create
 ThreadDied -> do
 -- Sanity check: if the thread has died, there is a chance
 -- that event manager is still alive. This could happend during
 -- the fork, for example. In this case we should clean up
 -- open pipes and everything else related to the event manager.
 -- See #4449
 mem <- readIORef timerManager
 _ <- case mem of
 Nothing -> return ()
 Just em -> TM.cleanup em
 create
 _other -> return st

shutdownManagers :: IO ()
shutdownManagers =
 withMVar ioManagerLock $ \_ -> do
 eventManagerArray <- readIORef eventManager
 let (_, high) = boundsIOArray eventManagerArray
 forM_ [0..high] $ \i -> do
 mmgr <- readIOArray eventManagerArray i
 case mmgr of
 Nothing -> return ()
 Just (_,mgr) -> M.shutdown mgr

foreign import ccall unsafe "rtsSupportsBoundThreads" threaded :: Bool

ioManagerCapabilitiesChanged :: IO ()
ioManagerCapabilitiesChanged = do
 withMVar ioManagerLock $ \_ -> do
 new_n_caps <- getNumCapabilities
 numEnabled <- readIORef numEnabledEventManagers
 writeIORef numEnabledEventManagers new_n_caps
 eventManagerArray <- readIORef eventManager
 let (_, high) = boundsIOArray eventManagerArray
 let old_n_caps = high + 1
 if new_n_caps > old_n_caps
 then do new_eventManagerArray <- newIOArray (0, new_n_caps - 1) Nothing

 -- copy the existing values into the new array:
 forM_ [0..high] $ \i -> do
 Just (tid,mgr) <- readIOArray eventManagerArray i
 if i < numEnabled
 then writeIOArray new_eventManagerArray i (Just (tid,mgr))
 else do tid' <- restartPollLoop mgr i
 writeIOArray new_eventManagerArray i (Just (tid',mgr))

 -- create new IO managers for the new caps:
 forM_ [old_n_caps..new_n_caps-1] $
 startIOManagerThread new_eventManagerArray

 -- update the event manager array reference:
 writeIORef eventManager new_eventManagerArray
 else when (new_n_caps > numEnabled) $
 forM_ [numEnabled..new_n_caps-1] $ \i -> do
 Just (_,mgr) <- readIOArray eventManagerArray i
 tid <- restartPollLoop mgr i
 writeIOArray eventManagerArray i (Just (tid,mgr))