    {-# LINE 1 "libraries/base/GHC/Event/Poll.hsc" #-}
    {-# LANGUAGE Trustworthy #-}
    {-# LINE 2 "libraries/base/GHC/Event/Poll.hsc" #-}
    {-# LANGUAGE GeneralizedNewtypeDeriving
               , NoImplicitPrelude
               , BangPatterns
      #-}

    module GHC.Event.Poll
        (
          new
        , available
        ) where

    {-# LINE 14 "libraries/base/GHC/Event/Poll.hsc" #-}

    {-# LINE 26 "libraries/base/GHC/Event/Poll.hsc" #-}

    {-# LINE 27 "libraries/base/GHC/Event/Poll.hsc" #-}

    import Control.Concurrent.MVar (MVar, newMVar, swapMVar)
    import Data.Bits (Bits, FiniteBits, (.|.), (.&.))
    import Data.Word
    import Foreign.C.Types (CInt(..), CShort(..))
    import Foreign.Ptr (Ptr)
    import Foreign.Storable (Storable(..))
    import GHC.Base
    import GHC.Conc.Sync (withMVar)
    import GHC.Enum (maxBound)
    import GHC.Num (Num(..))
    import GHC.Real (ceiling, fromIntegral)
    import GHC.Show (Show)
    import System.Posix.Types (Fd(..))

    import qualified GHC.Event.Array as A
    import qualified GHC.Event.Internal as E

    available :: Bool
    available = True
    {-# INLINE available #-}

    data Poll = Poll {
          pollChanges :: {-# UNPACK #-} !(MVar (A.Array PollFd))
        , pollFd      :: {-# UNPACK #-} !(A.Array PollFd)
        }

    new :: IO E.Backend
    new = E.backend poll modifyFd modifyFdOnce (\_ -> return ()) `liftM`
          liftM2 Poll (newMVar =<< A.empty) A.empty

    modifyFd :: Poll -> Fd -> E.Event -> E.Event -> IO Bool
    modifyFd p fd oevt nevt =
      withMVar (pollChanges p) $ \ary -> do
        A.snoc ary $ PollFd fd (fromEvent nevt) (fromEvent oevt)
        return True

    modifyFdOnce :: Poll -> Fd -> E.Event -> IO Bool
    modifyFdOnce = error "modifyFdOnce not supported in Poll backend"

    reworkFd :: Poll -> PollFd -> IO ()
    reworkFd p (PollFd fd npevt opevt) = do
      let ary = pollFd p
      if opevt == 0
        then A.snoc ary $ PollFd fd npevt 0
        else do
          found <- A.findIndex ((== fd) . pfdFd) ary
          case found of
            Nothing        -> error "reworkFd: event not found"
            Just (i,_)
              | npevt /= 0 -> A.unsafeWrite ary i $ PollFd fd npevt 0
              | otherwise  -> A.removeAt ary i

    poll :: Poll
         -> Maybe E.Timeout
         -> (Fd -> E.Event -> IO ())
         -> IO Int
    poll p mtout f = do
      let a = pollFd p
      mods <- swapMVar (pollChanges p) =<< A.empty
      A.forM_ mods (reworkFd p)
      n <- A.useAsPtr a $ \ptr len ->
        E.throwErrnoIfMinus1NoRetry "c_poll" $
        case mtout of
          Just tout ->
            c_pollLoop ptr (fromIntegral len) (fromTimeout tout)
          Nothing   ->
            c_poll_unsafe ptr (fromIntegral len) 0
      when (n /= 0) $ do
        A.loop a 0 $ \i e -> do
          let r = pfdRevents e
          if r /= 0
            then do f (pfdFd e) (toEvent r)
                    let i' = i + 1
                    return (i', i' == n)
            else return (i, True)
      return (fromIntegral n)
      where
        -- The poll timeout is specified as an Int, but c_poll takes a CInt. These
        -- can't be safely coerced as on many systems (e.g. x86_64) CInt has a
        -- maxBound of (2^32 - 1), even though Int may have a significantly higher
        -- bound.
        --
        -- This function deals with timeouts greater than maxBound :: CInt, by
        -- looping until c_poll returns a non-zero value (0 indicates timeout
        -- expired) OR the full timeout has passed.
        c_pollLoop :: Ptr PollFd -> (Word32) -> Int -> IO CInt
    {-# LINE 114 "libraries/base/GHC/Event/Poll.hsc" #-}
        c_pollLoop ptr len tout
            | isShortTimeout = c_poll ptr len (fromIntegral tout)
            | otherwise = do
                result <- c_poll ptr len (fromIntegral maxPollTimeout)
                if result == 0
                   then c_pollLoop ptr len (fromIntegral (tout - maxPollTimeout))
                   else return result
            where
              -- maxPollTimeout is smaller than 0 IFF Int is smaller than CInt.
              -- This means any possible Int input to poll can be safely directly
              -- converted to CInt.
              isShortTimeout = tout <= maxPollTimeout || maxPollTimeout < 0

        -- We need to account for 3 cases:
        --     1. Int and CInt are of equal size.
        --     2. Int is larger than CInt
        --     3. Int is smaller than CInt
        --
        -- In case 1, the value of maxPollTimeout will be the maxBound of Int.
        --
        -- In case 2, the value of maxPollTimeout will be the maxBound of CInt,
        -- which is the largest value accepted by c_poll. This will result in
        -- c_pollLoop recursing if the provided timeout is larger.
        --
        -- In case 3, "fromIntegral (maxBound :: CInt) :: Int" will result in a
        -- negative Int. This will cause isShortTimeout to be true and result in
        -- the timeout being directly converted to a CInt.
        maxPollTimeout :: Int
        maxPollTimeout = fromIntegral (maxBound :: CInt)

    fromTimeout :: E.Timeout -> Int
    fromTimeout E.Forever     = -1
    fromTimeout (E.Timeout s) = ceiling $ 1000 * s

    data PollFd = PollFd {
          pfdFd      :: {-# UNPACK #-} !Fd
        , pfdEvents  :: {-# UNPACK #-} !Event
        , pfdRevents :: {-# UNPACK #-} !Event
        } deriving (Show)

    newtype Event = Event CShort
        deriving (Eq, Show, Num, Storable, Bits, FiniteBits)

    -- We have to duplicate the whole enum like this in order for the
    -- hsc2hs cross-compilation mode to work

    {-# LINE 168 "libraries/base/GHC/Event/Poll.hsc" #-}
    pollIn     :: Event
    pollIn     = Event 1
    pollOut    :: Event
    pollOut    = Event 4
    pollErr    :: Event
    pollErr    = Event 8
    pollHup    :: Event
    pollHup    = Event 16

    {-# LINE 174 "libraries/base/GHC/Event/Poll.hsc" #-}

    {-# LINE 175 "libraries/base/GHC/Event/Poll.hsc" #-}

    fromEvent :: E.Event -> Event
    fromEvent e = remap E.evtRead  pollIn .|.
                  remap E.evtWrite pollOut
      where remap evt to
                | e `E.eventIs` evt = to
                | otherwise         = 0

    toEvent :: Event -> E.Event
    toEvent e = remap (pollIn .|. pollErr .|. pollHup)  E.evtRead `mappend`
                remap (pollOut .|. pollErr .|. pollHup) E.evtWrite
      where remap evt to
                | e .&. evt /= 0 = to
                | otherwise      = mempty

    instance Storable PollFd where
        sizeOf _    = (8)
    {-# LINE 192 "libraries/base/GHC/Event/Poll.hsc" #-}
        alignment _ = alignment (undefined :: CInt)

        peek ptr = do
          fd <- (\hsc_ptr -> peekByteOff hsc_ptr 0) ptr
    {-# LINE 196 "libraries/base/GHC/Event/Poll.hsc" #-}
          events <- (\hsc_ptr -> peekByteOff hsc_ptr 4) ptr
    {-# LINE 197 "libraries/base/GHC/Event/Poll.hsc" #-}
          revents <- (\hsc_ptr -> peekByteOff hsc_ptr 6) ptr
    {-# LINE 198 "libraries/base/GHC/Event/Poll.hsc" #-}
          let !pollFd' = PollFd fd events revents
          return pollFd'

        poke ptr p = do
          (\hsc_ptr -> pokeByteOff hsc_ptr 0) ptr (pfdFd p)
    {-# LINE 203 "libraries/base/GHC/Event/Poll.hsc" #-}
          (\hsc_ptr -> pokeByteOff hsc_ptr 4) ptr (pfdEvents p)
    {-# LINE 204 "libraries/base/GHC/Event/Poll.hsc" #-}
          (\hsc_ptr -> pokeByteOff hsc_ptr 6) ptr (pfdRevents p)
    {-# LINE 205 "libraries/base/GHC/Event/Poll.hsc" #-}

    foreign import ccall safe "poll.h poll"
        c_poll :: Ptr PollFd -> (Word32) -> CInt -> IO CInt
    {-# LINE 208 "libraries/base/GHC/Event/Poll.hsc" #-}

    foreign import ccall unsafe "poll.h poll"
        c_poll_unsafe :: Ptr PollFd -> (Word32) -> CInt -> IO CInt
    {-# LINE 211 "libraries/base/GHC/Event/Poll.hsc" #-}

    {-# LINE 212 "libraries/base/GHC/Event/Poll.hsc" #-}