Re: [wxhaskell-users] Some WX questions - a couple of missing bindings and a segfault

[Jules B. <ju...@je...>]

Eric Kow wrote:
> Hi Jules,
> 
> Is this the same bug as this one from the Tracker?
>   http://sourceforge.net/tracker/index.php?func=detail&aid=1003006&group_id=73133&atid=536845
> 
> (was submitted by Paul Johnson, I think)
> 
> Also, if you are so inclined, it would be extra-helpful if you could
> submit your demonstrator as a test case in the bugs/ directory (darcs
> send).  It would be extra-extra-helpful if you could work out a way to
> reproduce this bug very consistently (for example, by repeatedly
> loading the image in or something)

Hi Eric,

It does look like it could well be the same bug. Although seems 
surprising for there to be a hole in the memory? Perhaps it is being 
moved by GC... but GC doesn't move memory which was allocated by a C(++) 
library does it?

I can reproduce the bug simply by creating images over and over and over 
again.

Here is a fairly minimal testcase, at the bottom of this mail. It always 
seems to segfault for me, normally after about 5 iterations, sometimes 
as many as 22.

It's interesting that there is a very long pause before the segfault. 
That is, one iteration of creating an image is normally a tiny tiny 
fraction of a second, but if it's going to segfault, there is a long pause.

I tried running with -Sstderr to see if I could see an obvious link 
between garbage collections and crashes, but if there is one it isn't 
obvious to me!

Happy to try more stuff to pin this down, let me know what I can do.

Jules

import qualified Graphics.UI.WX as WX
import Graphics.UI.WXCore.Image
import Graphics.UI.WXCore.Draw
import Graphics.UI.WXCore.WxcClassesAL
import Graphics.UI.WXCore.WxcClassesMZ

import Foreign
import Data.Word

import Control.Monad

main = do
   forM_ [0..500]
     (\i -> putStrLn ("Iteration : " ++ show i) >> createAndGetPixels)

createAndGetPixels = do
   bmp <- bitmapCreateEmpty (WX.Size 256 256) 24
   pixelsFromBitmap bmp

pixelsFromBitmap bmp = do
     image <- imageCreateFromBitmap bmp
     pixels <- imageGetData image
     putStrLn $ "pixels : " ++ show pixels
     bytes <- peekArray 8 (castPtr pixels)
     putStrLn $ "bytes : " ++ show (bytes :: [Word8])
     WX.Size w h <- imageGetSize image
     putStrLn $ "Image size : " ++ show (w,h)
     pixs <- imageGetPixels image
     putStrLn $ "number of pixs = " ++ show (length pixs)
     putStrLn $ "first pixel " ++ show (head pixs)