[project @ 2004-02-12 21:23:48 by krasimir]

[ghc-base.git] / GHC / TopHandler.lhs

diff --git a/GHC/TopHandler.lhs b/GHC/TopHandler.lhs
index 7750566..884fcf1 100644 (file)
--- a/GHC/TopHandler.lhs
+++ b/GHC/TopHandler.lhs
@@ -9,82 +9,76 @@
 -- Stability   :  internal
 -- Portability :  non-portable (GHC Extensions)
 --
--- Top-level IO actions want to catch exceptions (e.g., 'forkIO' and 
--- 'GHC.Main.mainIO') and report them - 'topHandler' is the exception
--- handler they should use for this.
+-- Support for catching exceptions raised during top-level computations
+-- (e.g. @Main.main@, 'Control.Concurrent.forkIO', and foreign exports)
 --
 -----------------------------------------------------------------------------
 
 module GHC.TopHandler (
-   runMain, reportStackOverflow, reportError 
+   runIO, runNonIO, reportStackOverflow, reportError
   ) where
 
 import Prelude
 
 import System.IO
+import Control.Exception
 
 import Foreign.C.String
 import Foreign.Ptr
 import GHC.IOBase
 import GHC.Exception
+import GHC.Prim (unsafeCoerce#)
 
--- runMain is applied to Main.main by TcModule
-runMain :: IO a -> IO ()
-runMain main = catchException (main >> return ()) topHandler
-  
-topHandler :: Exception -> IO ()
+-- | 'runIO' is wrapped around @Main.main@ by @TcModule@.  It is also 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 = catchException main topHandler
+
+-- | 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 = catchException (a `seq` return a) topHandler
+
+topHandler :: Exception -> IO a
 topHandler err = catchException (real_handler err) topHandler
 
 -- Make sure we handle errors while reporting the error!
 -- (e.g. evaluating the string passed to 'error' might generate
 --  another error, etc.)
 --
-real_handler :: Exception -> IO ()
+real_handler :: Exception -> IO a
 real_handler ex =
   case ex of
        AsyncException StackOverflow -> reportStackOverflow True
 
        -- only the main thread gets ExitException exceptions
-       ExitException ExitSuccess     -> shutdownHaskellAndExit 0
-       ExitException (ExitFailure n) -> shutdownHaskellAndExit n
-
-       Deadlock    -> reportError True 
-                       "no threads to run:  infinite loop or deadlock?"
-  
-       ErrorCall s -> reportError True s
-       other       -> reportError True (showsPrec 0 other "\n")
+       ExitException ExitSuccess     -> safe_exit 0
+       ExitException (ExitFailure n) -> safe_exit n
 
--- NOTE: shutdownHaskellAndExit must be called "safe", because it *can*
--- re-enter Haskell land through finalizers.
-foreign import ccall "shutdownHaskellAndExit" 
-  shutdownHaskellAndExit :: Int -> IO ()
+       other       -> reportError True other
+          
 
-reportStackOverflow :: Bool -> IO ()
+reportStackOverflow :: Bool -> IO a
 reportStackOverflow bombOut = do
    (hFlush stdout) `catchException` (\ _ -> return ())
    callStackOverflowHook
-   if bombOut then
-     stg_exit 2
-    else
-     return ()
+   if bombOut 
+       then exit 2
+       else return undefined
 
-reportError :: Bool -> String -> IO ()
-reportError bombOut str = do
-   (hFlush stdout) `catchException` (\ _ -> return ())
-   withCStringLen str $ \(cstr,len) -> do
-     writeErrString errorHdrHook cstr len
-     if bombOut 
-       then stg_exit 1
-        else return ()
-
-#ifndef ILX
-foreign import ccall "&ErrorHdrHook" errorHdrHook :: Ptr ()
-#else
-foreign import ccall "ErrorHdrHook" errorHdrHook :: Ptr ()
-#endif
-
-foreign import ccall unsafe "writeErrString__"
-       writeErrString :: Ptr () -> CString -> Int -> IO ()
+reportError :: Bool -> Exception -> IO a
+reportError bombOut ex = do
+   handler <- getUncatchedExceptionHandler
+   handler ex
+   if bombOut
+      then exit 1
+      else return undefined
 
 -- SUP: Are the hooks allowed to re-enter Haskell land?  If so, remove
 -- the unsafe below.
@@ -93,4 +87,17 @@ foreign import ccall unsafe "stackOverflow"
 
 foreign import ccall unsafe "stg_exit"
        stg_exit :: Int -> IO ()
+
+exit :: Int -> IO a
+exit r = unsafeCoerce# (stg_exit r)
+
+-- NOTE: shutdownHaskellAndExit must be called "safe", because it *can*
+-- re-enter Haskell land through finalizers.
+foreign import ccall "shutdownHaskellAndExit" 
+  shutdownHaskellAndExit :: Int -> IO ()
+
+-- 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.
+safe_exit :: Int -> IO a
+safe_exit r = unsafeCoerce# (shutdownHaskellAndExit r)
 \end{code}