\begin{code}
{-# OPTIONS_GHC -XNoImplicitPrelude #-}
{-# OPTIONS_GHC -fno-warn-unused-imports #-}
{-# OPTIONS_HADDOCK hide #-}
-----------------------------------------------------------------------------
-- |
-- Module      :  GHC.TopHandler
-- Copyright   :  (c) The University of Glasgow, 2001-2002
-- License     :  see libraries/base/LICENSE
-- 
-- Maintainer  :  cvs-ghc@haskell.org
-- Stability   :  internal
-- Portability :  non-portable (GHC Extensions)
--
-- Support for catching exceptions raised during top-level computations
-- (e.g. @Main.main@, 'Control.Concurrent.forkIO', and foreign exports)
--
-----------------------------------------------------------------------------

-- #hide
module GHC.TopHandler (
   runMainIO, runIO, runIOFastExit, runNonIO,
   topHandler, topHandlerFastExit,
   reportStackOverflow, reportError,
  ) where

import Control.Exception
import Data.Maybe
import Data.Dynamic (toDyn)

import Foreign
import Foreign.C
import GHC.Base
import GHC.Conc hiding (throwTo)
import GHC.Num
import GHC.Real
import GHC.Handle
import GHC.IOBase
--import GHC.Weak
import Data.Typeable
#if defined(mingw32_HOST_OS)
import GHC.ConsoleHandler
#endif

-- | 'runMainIO' is wrapped around 'Main.main' (or whatever main is
-- called in the program).  It catches otherwise uncaught exceptions,
-- and also flushes stdout\/stderr before exiting.
runMainIO :: IO a -> IO a
runMainIO main = 
    do 
      {-main_thread_id <- myThreadId
      weak_tid <- mkWeakThreadId main_thread_id
      install_interrupt_handler $ do
           m <- deRefWeak weak_tid 
           case m of
               Nothing  -> return ()
               Just tid -> throwTo tid (toException UserInterrupt)-}
      a <- main
      cleanUp
      return a
    `catch`
      topHandler

install_interrupt_handler :: IO () -> IO ()
#ifdef mingw32_HOST_OS
install_interrupt_handler handler = do
  GHC.ConsoleHandler.installHandler $
     Catch $ \event -> 
        case event of
           ControlC -> handler
           Break    -> handler
           Close    -> handler
           _ -> return ()
  return ()
#else
-- #include "Signals.h"
-- specialised version of System.Posix.Signals.installHandler, which
-- isn't available here.
install_interrupt_handler handler = do
   --let sig = CONST_SIGINT :: CInt
   --setHandler sig (Just (const handler, toDyn handler))
   --stg_sig_install sig STG_SIG_RST nullPtr
     -- STG_SIG_RST: the second ^C kills us for real, just in case the
     -- RTS or program is unresponsive.
   return ()

foreign import ccall unsafe
  stg_sig_install
	:: CInt				-- sig no.
	-> CInt				-- action code (STG_SIG_HAN etc.)
	-> Ptr ()			-- (in, out) blocked
	-> IO CInt			-- (ret) old action code
#endif

-- make a weak pointer to a ThreadId: holding the weak pointer doesn't
-- keep the thread alive and prevent it from being identified as
-- deadlocked.  Vitally important for the main thread.
{-
mkWeakThreadId :: ThreadId -> IO (Weak ThreadId)
mkWeakThreadId t@(ThreadId t#) = IO $ \s ->
   case mkWeak# t# t (unsafeCoerce# 0#) s of 
      (# s1, w #) -> (# s1, Weak w #)
-}
-- | 'runIO' is wrapped around every @foreign export@ and @foreign
-- import \"wrapper\"@ to mop up any uncaught exceptions.  Thus, the
-- result of running 'System.Exit.exitWith' in a foreign-exported
-- function is the same as in the main thread: it terminates the
-- program.
--
runIO :: IO a -> IO a
runIO main = catch main topHandler

-- | Like 'runIO', but in the event of an exception that causes an exit,
-- we don't shut down the system cleanly, we just exit.  This is
-- useful in some cases, because the safe exit version will give other
-- threads a chance to clean up first, which might shut down the
-- system in a different way.  For example, try 
--
--   main = forkIO (runIO (exitWith (ExitFailure 1))) >> threadDelay 10000
--
-- This will sometimes exit with "interrupted" and code 0, because the
-- main thread is given a chance to shut down when the child thread calls
-- safeExit.  There is a race to shut down between the main and child threads.
--
runIOFastExit :: IO a -> IO a
runIOFastExit main = catch main topHandlerFastExit
        -- NB. this is used by the testsuite driver

-- | The same as 'runIO', but for non-IO computations.  Used for
-- wrapping @foreign export@ and @foreign import \"wrapper\"@ when these
-- are used to export Haskell functions with non-IO types.
--
runNonIO :: a -> IO a
runNonIO a = catch (a `seq` return a) topHandler

topHandler :: SomeException -> IO a
topHandler err = catch (real_handler safeExit err) topHandler

topHandlerFastExit :: SomeException -> IO a
topHandlerFastExit err = 
  catchException (real_handler fastExit err) topHandlerFastExit

-- Make sure we handle errors while reporting the error!
-- (e.g. evaluating the string passed to 'error' might generate
--  another error, etc.)
--
real_handler :: (Int -> IO a) -> SomeException -> IO a
real_handler exit se@(SomeException exn) =
  cleanUp >>
  case cast exn of
      Just StackOverflow -> do
           reportStackOverflow
           exit 2

      Just UserInterrupt  -> exitInterrupted

      _ -> case cast exn of
           -- only the main thread gets ExitException exceptions
           Just ExitSuccess     -> exit 0
           Just (ExitFailure n) -> exit n

           _ -> do reportError se
                   exit 1
           

-- try to flush stdout/stderr, but don't worry if we fail
-- (these handles might have errors, and we don't want to go into
-- an infinite loop).
cleanUp :: IO ()
cleanUp = do
  hFlush stdout `catchAny` \_ -> return ()
  hFlush stderr `catchAny` \_ -> return ()

-- we have to use unsafeCoerce# to get the 'IO a' result type, since the
-- compiler doesn't let us declare that as the result type of a foreign export.
safeExit :: Int -> IO a
safeExit r = unsafeCoerce# (shutdownHaskellAndExit $ fromIntegral r)

exitInterrupted :: IO a
exitInterrupted = 
#ifdef mingw32_HOST_OS
  safeExit 252
#else
  -- we must exit via the default action for SIGINT, so that the
  -- parent of this process can take appropriate action (see #2301)
  --unsafeCoerce# (shutdownHaskellAndSignal CONST_SIGINT)
  error "exitInterrupted"

foreign import ccall "shutdownHaskellAndSignal"
  shutdownHaskellAndSignal :: CInt -> IO ()
#endif

-- NOTE: shutdownHaskellAndExit must be called "safe", because it *can*
-- re-enter Haskell land through finalizers.
foreign import ccall "Rts.h shutdownHaskellAndExit"
  shutdownHaskellAndExit :: CInt -> IO ()

fastExit :: Int -> IO a
fastExit r = unsafeCoerce# (stg_exit (fromIntegral r))

foreign import ccall "Rts.h stg_exit"
  stg_exit :: CInt -> IO ()
\end{code}