MonoTouch SIGSEGV during garbage collector initiated Dispose on ABPeoplePickerNavigationController - ios

Question

Building against MT 6.0.4.
Targeting iOS 4.
Testing on an iPhone 4S.
I'm stumped as to what I am doing wrong. I display the ABPeoplePickerNavigationController modally after subscribing to the SelectPerson event. Within the event, I take a copy of the data I need (only holding references to strings, not to any of the AdressBook or Person instances), and then close the modal dialog:
private string selectedPersonFirstName;
private string selectedPersonEmail;
private string selectedPersonPhone;
private void SelectContact()
{
var peoplePicker = new ABPeoplePickerNavigationController();
peoplePicker.Cancelled += (sender, e) =>
{
selectedPersonFirstName = null;
selectedPersonEmail = null;
selectedPersonPhone = null;
peoplePicker.DismissViewController(true, null);
};
peoplePicker.SelectPerson += (sender, e) =>
{
var selectedName = String.Format("{0} {1}", e.Person.FirstName, e.Person.LastName);
selectedPersonFirstName = e.Person.FirstName;
if ( e.Person.GetEmails().Count > 0)
selectedPersonEmail = e.Person.GetEmails().FirstOrDefault().Value;
if ( e.Person.GetPhones().Count > 0)
selectedPersonPhone = e.Person.GetPhones().FirstOrDefault().Value;
peoplePicker.DismissViewController(true, null);
};
PresentViewController(peoplePicker, true, null);
}
At some point later when the GC kicks in, it crashes:
Stacktrace:
at MonoTouch.Foundation.NSObject.FinishDispose () [0x0000b] in /Developer/MonoTouch/Source/monotouch/src/Foundation/NSObject.cs:158
at MonoTouch.Foundation.NSObject/MonoTouch_Disposer.Drain (MonoTouch.Foundation.NSObject) [0x00062] in /Developer/MonoTouch/Source/monotouch/src/Foundation/NSObject.cs:376
at (wrapper runtime-invoke) object.runtime_invoke_dynamic (intptr,intptr,intptr,intptr) <0xffffffff>
at MonoTouch.UIKit.UIApplication.Main (string[],string,string) [0x0004c] in /Developer/MonoTouch/Source/monotouch/src/UIKit/UIApplication.cs:38
at MyApp.iOS.Application.Main (string[]) [0x00000] in /Users/tyson/Code/MyApp/iOS/Main.cs:19
at (wrapper runtime-invoke) object.runtime_invoke_dynamic (intptr,intptr,intptr,intptr) <0xffffffff>
Native stacktrace:
0 MyAppName--------------- 0x00f574f4 mono_handle_native_sigsegv + 280
1 MyAppName--------------- 0x00f3a2b8 mono_sigsegv_signal_handler + 268
2 libsystem_c.dylib 0x31ae97ed _sigtramp + 48
3 CoreFoundation 0x3745b2e7 CFRelease + 94
4 AddressBookUI 0x373922d1 -[ABGroupWrapper dealloc] + 100
5 libobjc.A.dylib 0x35a14175 _objc_rootRelease + 36
6 AddressBookUI 0x373a3f57 -[ABModel dealloc] + 146
7 libobjc.A.dylib 0x35a14175 _objc_rootRelease + 36
8 AddressBookUI 0x373aec43 -[ABAbstractViewController dealloc] + 38
9 AddressBookUI 0x373aeb3d -[ABMembersViewController dealloc] + 216
10 libobjc.A.dylib 0x35a14175 _objc_rootRelease + 36
11 CoreFoundation 0x3745b2e7 CFRelease + 94
12 CoreFoundation 0x3747106b -[__NSArrayM dealloc] + 122
13 libobjc.A.dylib 0x35a14175 _objc_rootRelease + 36
14 UIKit 0x33c891b9 -[UIViewController dealloc] + 496
15 UIKit 0x33c88f2f -[UINavigationController dealloc] + 198
16 AddressBookUI 0x373adcbd -[ABPeoplePickerNavigationController dealloc] + 376
17 libobjc.A.dylib 0x35a14175 _objc_rootRelease + 36
18 MyAppName--------------- 0x001e1ccc wrapper_managed_to_native_MonoTouch_ObjCRuntime_Messaging_void_objc_msgSend_intptr_intptr + 68
19 MyAppName--------------- 0x001ad49c MonoTouch_Foundation_NSObject_MonoTouch_Disposer_Drain_MonoTouch_Foundation_NSObject + 364
20 MyAppName--------------- 0x006997b8 wrapper_runtime_invoke_object_runtime_invoke_dynamic_intptr_intptr_intptr_intptr + 200
21 MyAppName--------------- 0x00f3c6a4 mono_jit_runtime_invoke + 1644
22 MyAppName--------------- 0x00ff5dc0 mono_runtime_invoke + 128
23 MyAppName--------------- 0x00f2c6ec native_to_managed_trampoline_MonoTouch_Foundation_NSObject_MonoTouch_Disposer_Drain + 280
24 CoreFoundation 0x374a0eef +[NSObject performSelector:withObject:] + 42
25 Foundation 0x37d51747 __NSThreadPerformPerform + 350
26 CoreFoundation 0x374e6ad3 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 14
27 CoreFoundation 0x374e629f __CFRunLoopDoSources0 + 214
28 CoreFoundation 0x374e5045 __CFRunLoopRun + 652
29 CoreFoundation 0x374684a5 CFRunLoopRunSpecific + 300
30 CoreFoundation 0x3746836d CFRunLoopRunInMode + 104
31 GraphicsServices 0x32375439 GSEventRunModal + 136
32 UIKit 0x33bece7d UIApplicationMain + 1080
33 MyAppName--------------- 0x001e6ca4 wrapper_managed_to_native_MonoTouch_UIKit_UIApplication_UIApplicationMain_int_string___intptr_intptr + 240
34 MyAppName--------------- 0x00ee0210 MyApp_iOS_Application_Main_string__ + 152
35 MyAppName--------------- 0x006997b8 wrapper_runtime_invoke_object_runtime_invoke_dynamic_intptr_intptr_intptr_intptr + 200
36 MyAppName--------------- 0x00f3c6a4 mono_jit_runtime_invoke + 1644
37 MyAppName--------------- 0x00ff5dc0 mono_runtime_invoke + 128
38 MyAppName--------------- 0x00ffa224 mono_runtime_exec_main + 436
39 MyAppName--------------- 0x00fff770 mono_runtime_run_main + 756
40 MyAppName--------------- 0x00f434a4 mono_jit_exec + 140
41 MyAppName--------------- 0x0105c04c main + 2028
42 MyAppName--------------- 0x0001bd18 start + 40
=================================================================
Got a SIGSEGV while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries
used by your application.
=================================================================
Has anyone seen anything like this before? I'm up for workarounds at this point as I need it more reliable for a demo ASAP (not for app store submission yet).

Answer 1

It looks like a bug. Something gets released one time too many and crash.
You can, for your demonstration purpose, work around it by defining CFRetain like this:
[System.Runtime.InteropServices.DllImport ("/System/Library/Frameworks/CoreFoundation.framework/CoreFoundation")]
static extern IntPtr CFRetain (IntPtr obj);
and use it on the _AddressBook, like that
peoplePicker.SelectPerson += (sender, e) => {
CFRetain (peoplePicker._AddressBook);
var selectedName = String.Format("{0} {1}", e.Person.FirstName, e.Person.LastName);
...
That will balance the count and avoid the crash.
Update: bug filled, you can c.c. yourself the the bug report to know when a fix will be released.