Re: [Gtk2hs-users] Problem on OS X

[Chris K. <ha...@li...>]

Any ideas why this could be dying?

I have tracked down where the Segmentation Fault is being emitted from.
 The new test case has a traced version of layoutGetDrawWindow and
makeNewGObject' showing the problem is triggered in objectRef:

> -- The Graphics.UI.Gtk.Types is usually hidden, I modified gtk.cabal to expose it
> import Graphics.UI.Gtk.Types(objectRef,objectUnrefFromMainloop,unLayout
>                             ,DrawWindow(DrawWindow))
> import Graphics.UI.Gtk(initGUI,windowNew,layoutNew,layoutGetDrawWindow,containerAdd,widgetShowAll,mainIteration
>                       ,GObjectClass,Layout)
> import Foreign(newForeignPtr,withForeignPtr,nullPtr,peekByteOff,castPtr
>               ,FinalizerPtr,ForeignPtr,Ptr)
> import Control.Exception(evaluate)
> import Control.Monad(when)
> import Debug.Trace(trace)
> 
> makeNewGObject' :: GObjectClass obj
>                 => (ForeignPtr obj -> obj, FinalizerPtr obj) -- ^ constructor for the Haskell object and finalizer C function
>                 -> IO (Ptr obj) -- ^ action which yields a pointer to the C object
>                 -> IO obj
> makeNewGObject' (constr, objectUnref) generator = trace "makeNewGObject' evaluated" $ do
>   trace "makeNewGObject' running" $ do
>   objPtr <- generator
>   trace ("generator returned "++show objPtr) $ do
>   when (objPtr == nullPtr) (fail "makeNewGObject: object is NULL")
>   trace ("before objectRef "++show objPtr) $ do
>   objectRef objPtr
> --  obj <- newForeignPtr objPtr objectUnref
>   trace ("before newForeignPtr "++show objPtr) $ do
>   obj <- flip newForeignPtr objPtr objectUnref
>   trace ("before constr"++show obj) $ do
>   thing <- evaluate (constr obj)
>   trace ("made thing") $ do
>   return thing
> 
> mkDrawWindow' = trace "mkDrawWindow'" (dw'', o')
>   where dw' x = trace ("my DrawWindow "++show x) $ DrawWindow x
>         dw''= trace ("trace dw'") dw'
>         o' = trace ("trace objectUnrefFromMainloop") objectUnrefFromMainloop
> 
> layoutGetDrawWindow' :: Layout -> IO DrawWindow
> layoutGetDrawWindow' lay = makeNewGObject' (trace "hi" mkDrawWindow') $ trace "operate" $ 
>   withForeignPtr (unLayout lay) $ \lay' -> do
>     trace (show lay') $ do
>     bin_window <- peekByteOff lay' 144
>     trace (show bin_window) $ do
>     return (castPtr bin_window)
> 
> main = do
>   initGUI
>   window <- windowNew
>   layout <- layoutNew Nothing Nothing
>   containerAdd window layout
>   widgetShowAll window
>   b <- mainIteration
>   trace (show b) $ do
>   dw <- layoutGetDrawWindow' layout
>   return ()

The output produced is

> shell> ghc --make trim2.hs  && ./trim2
> [1 of 1] Compiling Main             ( trim2.hs, trim2.o )
> Linking trim2 ...
> Xlib:  extension "RANDR" missing on display "/tmp/launch-UrBjlu/org.x:0".
> True
> hi
> mkDrawWindow'
> makeNewGObject' evaluated
> makeNewGObject' running
> operate
> 0x02061818
> 0x0145a80d
> generator returned 0x0145a80d
> before objectRef 0x0145a80d
> Segmentation fault

The glib-0.11.0/dist/build/System/Glib/GObject.hs contains objectRef as:

> -- | Increase the reference counter of an object
> --
> objectRef :: GObjectClass obj => Ptr obj -> IO ()
> objectRef obj = do
>   g_object_ref (castPtr obj)
>   return ()
> 
> foreign import ccall unsafe "g_object_ref"
>   g_object_ref :: ((Ptr ()) -> (IO (Ptr ())))

Any ideas why this could be dying?