Xamarin.Mac使SIGSEGV模糊

Question

I'm encountering an obscure segfault with xamarin.mac , this is the (unhelpful) stacktrace :

  at <unknown> <0xffffffff>
  at (wrapper managed-to-native) MonoMac.AppKit.NSApplication.NSApplicationMain     (int,string[]) <0xffffffff>
  at MonoMac.AppKit.NSApplication.Main (string[]) <0x00097>
  at gitbookpro.mac.MainClass.Main (string[]) <0x00017>
  at (wrapper runtime-invoke) <Module>.runtime_invoke_void_object (object,intptr,intptr,intptr) <0xffffffff>

The crash happens after handling an SelectionDidChange on an NSOutlineView which does a fair amount of processing.

It's hard to pin point what exactly is causing this crash.

Any ideas ?

Answer 1

The error was caused by, C# objects being wrongly garbaged collected .

They were garbage collected because those objects were being returned to objective-c code (native code), and since no reference was kept in the C# the garbage collector was deleting them.

This was what was happening :

1. create C# obj 2. return obj to native code 3. ... wait a little bit ... 4. turn native object back into to C# obj (in event handlers etc ...) 5. Access C# obj <= This would fail occasionally since it was being garbage collected during step #3

What you should do :

1. create C# obj 1bis. Keep an extra reference to the object somewhere (in an Dictionary for example) 2. return obj to native code 3. ... wait a little bit ... 4. turn native object back into to C# obj (in event handlers etc ...) 4bis. Remove extra reference 5. Access C# obj <= This would fail occasionally since it was being garbage collected during step #3

And that's it !