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Problems with GNUMail or GSDecorationView?

From: Tim Kack
Subject: Problems with GNUMail or GSDecorationView?
Date: Wed, 19 Aug 2009 10:38:19 +0200

Hi all,

I am quite amateur when it comes to development, but I really want to keep GNUMail alive as my primary email client.
So bear with me if this analysis is a bit thin.

While debugging why the closing the Compose window (by hitting X or clicking 'Send') generates a SIGSEGV, I found the following and I would like to know your opinions whether this is a bug in GNUstep gui classes or in GNUMail.

First some structures:
EditWindow is a subclass of NSWindow
EditWindowController is a subclass of NSWindowController.

The controller is has the following initializer, and it is not using NIBs on Linux so the method argument is not important right now:

- (id) initWithWindowNibName: (NSString *) windowNibName

It creates a window with:

theEditWindow = [[EditWindow alloc] initWithContentRect: NSMakeRect(50,75,750,520)
                      styleMask: (NSClosableWindowMask|NSTitledWindowMask|
                      backing: NSBackingStoreRetained
                      defer: NO];
  self = [super initWithWindow: theEditWindow];

It then sets itself to be the delegate:

  [theEditWindow setDelegate: self];

the controller is adding a Toolbar with the following setup and attaches it to the window

 // We initialize our toolbar
  aToolbar = [[NSToolbar alloc] initWithIdentifier: @"EditWindowToolbar"];
  [aToolbar setDelegate: self];
  [[self window] setToolbar: aToolbar];

With this known we know that:
* the EditWindow's delegate is the EditWindowController
* the toolbar in the EditWindow has the EditWindowController as delegate.

Now the problem:

When you hit 'Send' or close the window the following deallocation sequence is happening (ordered):
-dealloc in EditWindowController is called. (This goes fine)
-dealloc in EditWindow is called and crashes.

The crash is happening when  [super dealloc] is called and the following deallocation sequence is happening:
In NSWindow.m:734 -dealloc first thing that is called is [self setToolbar: nil];
It will try to remove the last toolbar view with (a  GSWindowDecorationView *_wv;) with removeToolbarView: [_toolbar _toolbarView].
The last method call in removeToolbarView is this:

[self changeWindowHeight: -toolbarViewHeight];

This is calling the follwing to adjust the frame in the NSWindow:

[window setFrame: windowFrame display: YES];

Here is the problem in the setFrame:display method that causes the sigsegv:

2067  if (NSEqualSizes(frameRect.size, _frame.size) == NO)
2068     {
2069       if ([_delegate respondsToSelector: @selector(windowWillResize:toSize:)])
2070         {
2071           frameRect.size = [_delegate windowWillResize: self
2072                                                 toSize: frameRect.size];
2073         }
2074     }

Note, at this point _delegate will be 0xdeadface because the EditWindowController has been deallocated and therefore respondsToSelector will crash.

Now, my question is - is this a GNUMail bug (i.e. the NSToolbar should have been deallocated earlier) or is it a problem with the GSWindowDecorationView removeToolbarView? Perhaps there should be a check if the delegate still is valid before calling setFrame?

The workaround is to set NSZombieEnabled to YES, but that will just hide the problem.

Any ideas?

Best regards,

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