[Mono-osx] Exception disposing of object

Jon Lipsky jon.lipsky at elevenworks.com
Wed Jun 13 18:31:04 UTC 2012

Hi All,

I'm getting random crashes in my MonoMac application in the "NSObject.MonoMac_Disposer.Drain" method:

 at (wrapper managed-to-native) MonoMac.ObjCRuntime.Messaging.void_objc_msgSendSuper (intptr,intptr) <IL 0x00024, 0xffffffff>
  at MonoMac.Foundation.NSObject/MonoMac_Disposer.Drain (MonoMac.Foundation.NSObject) [0x0003b] in /Development/github/monomac/src/Foundation/NSObject.cs
  at (wrapper dynamic-method) object.[MonoMac.Foundation.NSObject+MonoMac_Disposer.Void Drain(MonoMac.Foundation.NSObject)] (MonoMac.Foundation.NSObject,MonoMac.ObjCRuntime.Selector,MonoMac.Foundation.NSObject) <IL 0x00011, 0x0004b>
  at (wrapper native-to-managed) object.[MonoMac.Foundation.NSObject+MonoMac_Disposer.Void Drain(MonoMac.Foundation.NSObject)] (MonoMac.Foundation.NSObject,MonoMac.ObjCRuntime.Selector,MonoMac.Foundation.NSObject) <IL 0x000b6, 0xffffffff>
  at (wrapper managed-to-native) MonoMac.AppKit.NSApplication.NSApplicationMain (int,string[]) <IL 0x0009d, 0xffffffff>

By building my own version of MonoMac, I've been able to figure out that this crash always occurs when it's trying to dispose of the "super_handle" of my NSWindow subclass.

Has anyone seen this?  Am I doing something wrong, or could there possibly be an issue with MonoMac here?

It's quite easy to reproduce this issue:

1) Create a new MonoMac document based project.

2) Create a subclass of NSWindow:

using System;
using System.Collections.Generic;
using System.Drawing;
using MonoMac.AppKit;

namespace DisposalProblem
	public class TestWindow : NSWindow
		public TestWindow () : base(new RectangleF(100,100,500,500),NSWindowStyle.Resizable | NSWindowStyle.Closable, NSBackingStore.Buffered, false)
		public TestWindow (IntPtr aIntPtr) : base(aIntPtr)

3) Use interface builder to have one of the pull down menus send the message "showTestWindow:".

4) Add the following to your AppDelegate class:

		private TestWindow testWindow;
		public void ShowTestWindow()
			if (testWindow == null)
				testWindow = new TestWindow();
				testWindow.WillClose += HandleWillClose;

		void HandleWillClose (object sender, EventArgs e)
			testWindow.WillClose -= HandleWillClose;
			testWindow = null;

5) Run the application, and open and close the window using the "wired up" menu item.  Should take less than 20 seconds to make it crash.

Any help anyone could provide would be appreciated.


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