{-# LANGUAGE BangPatterns #-} {-# LANGUAGE CPP #-} {-# LANGUAGE ExistentialQuantification #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE NoImplicitPrelude #-} {-# LANGUAGE RecordWildCards #-} {-# LANGUAGE Trustworthy #-} -- | -- The event manager supports event notification on fds. Each fd may -- have multiple callbacks registered, each listening for a different -- set of events. Registrations may be automatically deactivated after -- the occurrence of an event ("one-shot mode") or active until -- explicitly unregistered. -- -- If an fd has only one-shot registrations then we use one-shot -- polling if available. Otherwise we use multi-shot polling. module GHC.Event.Manager ( -- * Types EventManager -- * Creation , new , newWith , newDefaultBackend -- * Running , finished , loop , step , shutdown , release , cleanup , wakeManager -- * State , callbackTableVar , emControl -- * Registering interest in I/O events , Lifetime (..) , Event , evtRead , evtWrite , IOCallback , FdKey(keyFd) , FdData , registerFd , unregisterFd_ , unregisterFd , closeFd , closeFd_ ) where #include "EventConfig.h" ------------------------------------------------------------------------ -- Imports import Control.Concurrent.MVar (MVar, newMVar, putMVar, tryPutMVar, takeMVar, withMVar) import Control.Exception (onException) import Data.Bits ((.&.)) import Data.Foldable (forM_) import Data.Functor (void) import Data.IORef (IORef, atomicModifyIORef', mkWeakIORef, newIORef, readIORef, writeIORef) import Data.Maybe (maybe) import Data.OldList (partition) import GHC.Arr (Array, (!), listArray) import GHC.Base import GHC.Conc.Sync (yield) import GHC.List (filter, replicate) import GHC.Num (Num(..)) import GHC.Real (fromIntegral) import GHC.Show (Show(..)) import GHC.Event.Control import GHC.Event.IntTable (IntTable) import GHC.Event.Internal (Backend, Event, evtClose, evtRead, evtWrite, Lifetime(..), EventLifetime, Timeout(..)) import GHC.Event.Unique (Unique, UniqueSource, newSource, newUnique) import System.Posix.Types (Fd) import qualified GHC.Event.IntTable as IT import qualified GHC.Event.Internal as I #if defined(HAVE_KQUEUE) import qualified GHC.Event.KQueue as KQueue #elif defined(HAVE_EPOLL) import qualified GHC.Event.EPoll as EPoll #elif defined(HAVE_POLL) import qualified GHC.Event.Poll as Poll #else # error not implemented for this operating system #endif ------------------------------------------------------------------------ -- Types data FdData = FdData { fdKey :: {-# UNPACK #-} !FdKey , fdEvents :: {-# UNPACK #-} !EventLifetime , _fdCallback :: !IOCallback } -- | A file descriptor registration cookie. data FdKey = FdKey { keyFd :: {-# UNPACK #-} !Fd , keyUnique :: {-# UNPACK #-} !Unique } deriving ( Eq -- ^ @since 4.4.0.0 , Show -- ^ @since 4.4.0.0 ) -- | Callback invoked on I/O events. type IOCallback = FdKey -> Event -> IO () data State = Created | Running | Dying | Releasing | Finished deriving ( Eq -- ^ @since 4.4.0.0 , Show -- ^ @since 4.4.0.0 ) -- | The event manager state. data EventManager = EventManager { emBackend :: !Backend , emFds :: {-# UNPACK #-} !(Array Int (MVar (IntTable [FdData]))) , emState :: {-# UNPACK #-} !(IORef State) , emUniqueSource :: {-# UNPACK #-} !UniqueSource , emControl :: {-# UNPACK #-} !Control , emLock :: {-# UNPACK #-} !(MVar ()) } -- must be power of 2 callbackArraySize :: Int callbackArraySize = 32 hashFd :: Fd -> Int hashFd fd = fromIntegral fd .&. (callbackArraySize - 1) {-# INLINE hashFd #-} callbackTableVar :: EventManager -> Fd -> MVar (IntTable [FdData]) callbackTableVar mgr fd = emFds mgr ! hashFd fd {-# INLINE callbackTableVar #-} haveOneShot :: Bool {-# INLINE haveOneShot #-} #if defined(darwin_HOST_OS) || defined(ios_HOST_OS) haveOneShot = False #elif defined(HAVE_EPOLL) || defined(HAVE_KQUEUE) haveOneShot = True #else haveOneShot = False #endif ------------------------------------------------------------------------ -- Creation handleControlEvent :: EventManager -> Fd -> Event -> IO () handleControlEvent mgr fd _evt = do msg <- readControlMessage (emControl mgr) fd case msg of CMsgWakeup -> return () CMsgDie -> writeIORef (emState mgr) Finished _ -> return () newDefaultBackend :: IO Backend #if defined(HAVE_KQUEUE) newDefaultBackend = KQueue.new #elif defined(HAVE_EPOLL) newDefaultBackend = EPoll.new #elif defined(HAVE_POLL) newDefaultBackend = Poll.new #else newDefaultBackend = errorWithoutStackTrace "no back end for this platform" #endif -- | Create a new event manager. new :: IO EventManager new = newWith =<< newDefaultBackend -- | Create a new 'EventManager' with the given polling backend. newWith :: Backend -> IO EventManager newWith be = do iofds <- fmap (listArray (0, callbackArraySize-1)) $ replicateM callbackArraySize (newMVar =<< IT.new 8) ctrl <- newControl False state <- newIORef Created us <- newSource _ <- mkWeakIORef state $ do st <- atomicModifyIORef' state $ \s -> (Finished, s) when (st /= Finished) $ do I.delete be closeControl ctrl lockVar <- newMVar () let mgr = EventManager { emBackend = be , emFds = iofds , emState = state , emUniqueSource = us , emControl = ctrl , emLock = lockVar } registerControlFd mgr (controlReadFd ctrl) evtRead registerControlFd mgr (wakeupReadFd ctrl) evtRead return mgr where replicateM n x = sequence (replicate n x) failOnInvalidFile :: String -> Fd -> IO Bool -> IO () failOnInvalidFile loc fd m = do ok <- m when (not ok) $ let msg = "Failed while attempting to modify registration of file " ++ show fd ++ " at location " ++ loc in errorWithoutStackTrace msg registerControlFd :: EventManager -> Fd -> Event -> IO () registerControlFd mgr fd evs = failOnInvalidFile "registerControlFd" fd $ I.modifyFd (emBackend mgr) fd mempty evs -- | Asynchronously shuts down the event manager, if running. shutdown :: EventManager -> IO () shutdown mgr = do state <- atomicModifyIORef' (emState mgr) $ \s -> (Dying, s) when (state == Running) $ sendDie (emControl mgr) -- | Asynchronously tell the thread executing the event -- manager loop to exit. release :: EventManager -> IO () release EventManager{..} = do state <- atomicModifyIORef' emState $ \s -> (Releasing, s) when (state == Running) $ sendWakeup emControl finished :: EventManager -> IO Bool finished mgr = (== Finished) `liftM` readIORef (emState mgr) cleanup :: EventManager -> IO () cleanup EventManager{..} = do writeIORef emState Finished void $ tryPutMVar emLock () I.delete emBackend closeControl emControl ------------------------------------------------------------------------ -- Event loop -- | Start handling events. This function loops until told to stop, -- using 'shutdown'. -- -- /Note/: This loop can only be run once per 'EventManager', as it -- closes all of its control resources when it finishes. loop :: EventManager -> IO () loop mgr@EventManager{..} = do void $ takeMVar emLock state <- atomicModifyIORef' emState $ \s -> case s of Created -> (Running, s) Releasing -> (Running, s) _ -> (s, s) case state of Created -> go `onException` cleanup mgr Releasing -> go `onException` cleanup mgr Dying -> cleanup mgr -- While a poll loop is never forked when the event manager is in the -- 'Finished' state, its state could read 'Finished' once the new thread -- actually runs. This is not an error, just an unfortunate race condition -- in Thread.restartPollLoop. See #8235 Finished -> return () _ -> do cleanup mgr errorWithoutStackTrace $ "GHC.Event.Manager.loop: state is already " ++ show state where go = do state <- step mgr case state of Running -> yield >> go Releasing -> putMVar emLock () _ -> cleanup mgr -- | To make a step, we first do a non-blocking poll, in case -- there are already events ready to handle. This improves performance -- because we can make an unsafe foreign C call, thereby avoiding -- forcing the current Task to release the Capability and forcing a context switch. -- If the poll fails to find events, we yield, putting the poll loop thread at -- end of the Haskell run queue. When it comes back around, we do one more -- non-blocking poll, in case we get lucky and have ready events. -- If that also returns no events, then we do a blocking poll. step :: EventManager -> IO State step mgr@EventManager{..} = do waitForIO state <- readIORef emState state `seq` return state where waitForIO = do n1 <- I.poll emBackend Nothing (onFdEvent mgr) when (n1 <= 0) $ do yield n2 <- I.poll emBackend Nothing (onFdEvent mgr) when (n2 <= 0) $ do _ <- I.poll emBackend (Just Forever) (onFdEvent mgr) return () ------------------------------------------------------------------------ -- Registering interest in I/O events -- | Register interest in the given events, without waking the event -- manager thread. The 'Bool' return value indicates whether the -- event manager ought to be woken. -- -- Note that the event manager is generally implemented in terms of the -- platform's @select@ or @epoll@ system call, which tend to vary in -- what sort of fds are permitted. For instance, waiting on regular files -- is not allowed on many platforms. registerFd_ :: EventManager -> IOCallback -> Fd -> Event -> Lifetime -> IO (FdKey, Bool) registerFd_ mgr@(EventManager{..}) cb fd evs lt = do u <- newUnique emUniqueSource let fd' = fromIntegral fd reg = FdKey fd u el = I.eventLifetime evs lt !fdd = FdData reg el cb (modify,ok) <- withMVar (callbackTableVar mgr fd) $ \tbl -> do oldFdd <- IT.insertWith (++) fd' [fdd] tbl let prevEvs :: EventLifetime prevEvs = maybe mempty eventsOf oldFdd el' :: EventLifetime el' = prevEvs `mappend` el case I.elLifetime el' of -- All registrations want one-shot semantics and this is supported OneShot | haveOneShot -> do ok <- I.modifyFdOnce emBackend fd (I.elEvent el') if ok then return (False, True) else IT.reset fd' oldFdd tbl >> return (False, False) -- We don't want or don't support one-shot semantics _ -> do let modify = prevEvs /= el' ok <- if modify then let newEvs = I.elEvent el' oldEvs = I.elEvent prevEvs in I.modifyFd emBackend fd oldEvs newEvs else return True if ok then return (modify, True) else IT.reset fd' oldFdd tbl >> return (False, False) -- this simulates behavior of old IO manager: -- i.e. just call the callback if the registration fails. when (not ok) (cb reg evs) return (reg,modify) {-# INLINE registerFd_ #-} -- | @registerFd mgr cb fd evs lt@ registers interest in the events @evs@ -- on the file descriptor @fd@ for lifetime @lt@. @cb@ is called for -- each event that occurs. Returns a cookie that can be handed to -- 'unregisterFd'. registerFd :: EventManager -> IOCallback -> Fd -> Event -> Lifetime -> IO FdKey registerFd mgr cb fd evs lt = do (r, wake) <- registerFd_ mgr cb fd evs lt when wake $ wakeManager mgr return r {-# INLINE registerFd #-} {- Building GHC with parallel IO manager on Mac freezes when compiling the dph libraries in the phase 2. As workaround, we don't use oneshot and we wake up an IO manager on Mac every time when we register an event. For more information, please read: https://gitlab.haskell.org/ghc/ghc/issues/7651 -} -- | Wake up the event manager. wakeManager :: EventManager -> IO () #if defined(darwin_HOST_OS) || defined(ios_HOST_OS) wakeManager mgr = sendWakeup (emControl mgr) #elif defined(HAVE_EPOLL) || defined(HAVE_KQUEUE) wakeManager _ = return () #else wakeManager mgr = sendWakeup (emControl mgr) #endif eventsOf :: [FdData] -> EventLifetime eventsOf [fdd] = fdEvents fdd eventsOf fdds = mconcat $ map fdEvents fdds -- | Drop a previous file descriptor registration, without waking the -- event manager thread. The return value indicates whether the event -- manager ought to be woken. unregisterFd_ :: EventManager -> FdKey -> IO Bool unregisterFd_ mgr@(EventManager{..}) (FdKey fd u) = withMVar (callbackTableVar mgr fd) $ \tbl -> do let dropReg = nullToNothing . filter ((/= u) . keyUnique . fdKey) fd' = fromIntegral fd pairEvents :: [FdData] -> IO (EventLifetime, EventLifetime) pairEvents prev = do r <- maybe mempty eventsOf `fmap` IT.lookup fd' tbl return (eventsOf prev, r) (oldEls, newEls) <- IT.updateWith dropReg fd' tbl >>= maybe (return (mempty, mempty)) pairEvents let modify = oldEls /= newEls when modify $ failOnInvalidFile "unregisterFd_" fd $ case I.elLifetime newEls of OneShot | I.elEvent newEls /= mempty, haveOneShot -> I.modifyFdOnce emBackend fd (I.elEvent newEls) _ -> I.modifyFd emBackend fd (I.elEvent oldEls) (I.elEvent newEls) return modify -- | Drop a previous file descriptor registration. unregisterFd :: EventManager -> FdKey -> IO () unregisterFd mgr reg = do wake <- unregisterFd_ mgr reg when wake $ wakeManager mgr -- | Close a file descriptor in a race-safe way. It might block, although for -- a very short time; and thus it is interruptible by asynchronous exceptions. closeFd :: EventManager -> (Fd -> IO ()) -> Fd -> IO () closeFd mgr close fd = do fds <- withMVar (callbackTableVar mgr fd) $ \tbl -> do prev <- IT.delete (fromIntegral fd) tbl case prev of Nothing -> close fd >> return [] Just fds -> do let oldEls = eventsOf fds when (I.elEvent oldEls /= mempty) $ do _ <- I.modifyFd (emBackend mgr) fd (I.elEvent oldEls) mempty wakeManager mgr close fd return fds forM_ fds $ \(FdData reg el cb) -> cb reg (I.elEvent el `mappend` evtClose) -- | Close a file descriptor in a race-safe way. -- It assumes the caller will update the callback tables and that the caller -- holds the callback table lock for the fd. It must hold this lock because -- this command executes a backend command on the fd. closeFd_ :: EventManager -> IntTable [FdData] -> Fd -> IO (IO ()) closeFd_ mgr tbl fd = do prev <- IT.delete (fromIntegral fd) tbl case prev of Nothing -> return (return ()) Just fds -> do let oldEls = eventsOf fds when (oldEls /= mempty) $ do _ <- I.modifyFd (emBackend mgr) fd (I.elEvent oldEls) mempty wakeManager mgr return $ forM_ fds $ \(FdData reg el cb) -> cb reg (I.elEvent el `mappend` evtClose) ------------------------------------------------------------------------ -- Utilities -- | Call the callbacks corresponding to the given file descriptor. onFdEvent :: EventManager -> Fd -> Event -> IO () onFdEvent mgr fd evs | fd == controlReadFd (emControl mgr) || fd == wakeupReadFd (emControl mgr) = handleControlEvent mgr fd evs | otherwise = do fdds <- withMVar (callbackTableVar mgr fd) $ \tbl -> IT.delete (fromIntegral fd) tbl >>= maybe (return []) (selectCallbacks tbl) forM_ fdds $ \(FdData reg _ cb) -> cb reg evs where -- | Here we look through the list of registrations for the fd of interest -- and sort out which match the events that were triggered. We, -- -- 1. re-arm the fd as appropriate -- 2. reinsert registrations that weren't triggered and multishot -- registrations -- 3. return a list containing the callbacks that should be invoked. selectCallbacks :: IntTable [FdData] -> [FdData] -> IO [FdData] selectCallbacks tbl fdds = do let -- figure out which registrations have been triggered matches :: FdData -> Bool matches fd' = evs `I.eventIs` I.elEvent (fdEvents fd') (triggered, notTriggered) = partition matches fdds -- sort out which registrations we need to retain isMultishot :: FdData -> Bool isMultishot fd' = I.elLifetime (fdEvents fd') == MultiShot saved = notTriggered ++ filter isMultishot triggered savedEls = eventsOf saved allEls = eventsOf fdds -- Reinsert multishot registrations. -- We deleted the table entry for this fd above so we there isn't a preexisting entry _ <- IT.insertWith (\_ _ -> saved) (fromIntegral fd) saved tbl case I.elLifetime allEls of -- we previously armed the fd for multiple shots, no need to rearm MultiShot | allEls == savedEls -> return () -- either we previously registered for one shot or the -- events of interest have changed, we must re-arm _ -> case I.elLifetime savedEls of OneShot | haveOneShot -> -- if there are no saved events and we registered with one-shot -- semantics then there is no need to re-arm unless (OneShot == I.elLifetime allEls && mempty == I.elEvent savedEls) $ void $ I.modifyFdOnce (emBackend mgr) fd (I.elEvent savedEls) _ -> -- we need to re-arm with multi-shot semantics void $ I.modifyFd (emBackend mgr) fd (I.elEvent allEls) (I.elEvent savedEls) return triggered nullToNothing :: [a] -> Maybe [a] nullToNothing [] = Nothing nullToNothing xs@(_:_) = Just xs unless :: Monad m => Bool -> m () -> m () unless p = when (not p)