Bug 14493 - Unregister Action<object> throws an NRE in 6.4.4.12 but not in 6.4.3.0
Summary: Unregister Action<object> throws an NRE in 6.4.4.12 but not in 6.4.3.0
Status: RESOLVED FIXED
Alias: None
Product: Runtime
Classification: Mono
Component: JIT ()
Version: unspecified
Hardware: Macintosh All
: --- major
Target Milestone: ---
Assignee: Bugzilla
URL:
: 14552 ()
Depends on:
Blocks:
 
Reported: 2013-09-06 15:13 UTC by Alexandre Pepin
Modified: 2013-09-09 11:16 UTC (History)
8 users (show)

Tags:
Is this bug a regression?: ---
Last known good build:

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Status:
RESOLVED FIXED

Description Alexandre Pepin 2013-09-06 15:13:52 UTC
Unregistering an Action<object> throws a "System.NullReferenceException: Object reference not set to an instance of an object". Sample :

Action<object> a = null;
a += Demo.Update;
a -= Demo.Update; // Crash here
public void Update(object o){ }

But, unregistering an Action (no parameters) or an Action<int> doesn't crash. It only crash when using an object as parameter. It was working on Xamarin.iOS 6.4.3.0
Comment 1 Sebastien Pouliot 2013-09-08 10:26:57 UTC
Confirmed. The NRE still happens when using the JIT (simulator) on the most recent monotouch (which is based on the mono 3.2.3 candidate hash revision).

Notes:
* it does not happen when the AOT compiler is used (i.e. works on device);
* it might explain a few recent bug reports where NRE occurs (only on 6.4.4, not 6.4.3)
Comment 2 Zoltan Varga 2013-09-09 05:42:00 UTC
I can't reproduce this, can somebody attach a complete test project ?
Comment 3 Sebastien Pouliot 2013-09-09 08:06:12 UTC
That's what I added to an existing unit test app to duplicate the issue. NRE happens when executing the last line (using simulator, fine on device).

+		public class Demo_14493 {
+			public void Update (object o)
+			{
+			}
+		}
+
+		[Test]
+		public void Action_14493 ()
+		{
+			var Demo = new Demo_14493 ();
+			Action<object> a = null;
+			a += Demo.Update;
+			a -= Demo.Update; // Crash here
+		}
Comment 4 Sebastien Pouliot 2013-09-09 08:41:40 UTC
A similar case was reported on the forum (with test case)

http://forums.xamarin.com/discussion/7766/nullreferenceexception-after-update-to-xamarin-ios-6-4-4-12#latest
Comment 5 Sebastien Pouliot 2013-09-09 09:18:39 UTC
Just like #14552 this works fine in Simulator/Release (JIT) but fails under Debug (JIT)
Comment 6 Zoltan Varga 2013-09-09 09:49:08 UTC
I can reproduce this now, it only happens while debugging.
Comment 7 Sebastien Pouliot 2013-09-09 09:51:31 UTC
hmm... at least that explains why automated testing on the bots did not catch this condition.
Comment 8 Zoltan Varga 2013-09-09 11:16:16 UTC
Fixed in mono master a918a647712b08f02ad5957a6d9019ee0030ea44.
Comment 9 Zoltan Varga 2013-09-09 11:16:38 UTC
*** Bug 14552 has been marked as a duplicate of this bug. ***