Bug 13858 - Got a SIGSEGV while executing native code
Summary: Got a SIGSEGV while executing native code
Alias: None
Product: Android
Classification: Xamarin
Component: Mono runtime / AOT Compiler ()
Version: 4.8.x
Hardware: PC Windows
: High normal
Target Milestone: ---
Assignee: Rodrigo Kumpera
: 14188 ()
Depends on: 14011 14013 14017 14019 14042 14043 14045 14050
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Reported: 2013-08-08 11:59 UTC by Allie Miller
Modified: 2015-09-08 05:48 UTC (History)
7 users (show)

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

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Description Allie Miller 2013-08-08 11:59:47 UTC
In a project with 2 activities, one activity calls the other one. In the second activity, a list is created with bitmaps. (normaly this is used in a ListView, with paging and dynamic calls to get these bitmaps)
When leaving the second activity, there is a  cleanup of the bitmaps. Then the Recycle() function is used and before  recycling, a test is run if its not already recycled.

When you come back in the first activity onRestart(), attempt GC.Collect() or a GC.Collect(GC.MaxGeneration) to help the garbage collector to cleanup the used bitmaps. Then it crashes. When removing the GC.Collect() it doesn’t crash. This crash did not occur in mono-android-4.6.08007 and does not throw the below error. However, after the update to 4.8.1., the following error occurs:

08-08 15:03:35.743: E/mono-rt(1600): Stacktrace:
08-08 15:03:35.743: E/mono-rt(1600): at <unknown> <0xffffffff>
08-08 15:03:35.743: E/mono-rt(1600): at (wrapper managed-to-native) object.wrapper_native_0x8233c760 (intptr,intptr,intptr) <IL 0x00025, 0xffffffff>
08-08 15:03:35.743: E/mono-rt(1600): at Android.Runtime.JNIEnv.CallVoidMethod (intptr,intptr) [0x00005] in /Users/builder/data/lanes/monodroid-mlion-monodroid-4.8.0-branch/b76e8ec4/source/monodroid/src/Mono.Android/src/Runtime/JNIEnv.g.cs:352
08-08 15:03:35.743: E/mono-rt(1600): at Android.Graphics.Bitmap.Recycle () [0x0002d] in /Users/builder/data/lanes/monodroid-mlion-monodroid-4.8.0-branch/b76e8ec4/source/monodroid/src/Mono.Android/platforms/android-10/src/generated/Android.Graphics.Bitmap.cs:682
08-08 15:03:35.743: E/mono-rt(1600): at bugImageViewRecycle.SecondActivity.clearCache () [0x00063] in c:\Users\IDUPPEN\Documents\Visual Studio 2012\Projects\bugImageViewRecycle\bugImageViewRecycle\SecondActivity.cs:69
08-08 15:03:35.743: E/mono-rt(1600): at bugImageViewRecycle.SecondActivity.OnDestroy () [0x00008] in c:\Users\IDUPPEN\Documents\Visual Studio 2012\Projects\bugImageViewRecycle\bugImageViewRecycle\SecondActivity.cs:56
08-08 15:03:35.743: E/mono-rt(1600): at Android.App.Activity.n_OnDestroy (intptr,intptr) [0x00008] in /Users/builder/data/lanes/monodroid-mlion-monodroid-4.8.0-branch/b76e8ec4/source/monodroid/src/Mono.Android/platforms/android-10/src/generated/Android.App.Activity.cs:1895
08-08 15:03:35.743: E/mono-rt(1600): at (wrapper dynamic-method) object.729d43ff-8c5e-4c81-a789-2a05b3a5f97b (intptr,intptr) <IL 0x00011, 0x0001b>
08-08 15:03:35.743: E/mono-rt(1600): at (wrapper native-to-managed) object.729d43ff-8c5e-4c81-a789-2a05b3a5f97b (intptr,intptr) <IL 0x00022, 0xffffffff>
08-08 15:03:35.743: E/mono-rt(1600): =================================================================
08-08 15:03:35.743: E/mono-rt(1600): Got a SIGSEGV while executing native code. This usually indicates
08-08 15:03:35.743: E/mono-rt(1600): a fatal error in the mono runtime or one of the native libraries
08-08 15:03:35.743: E/mono-rt(1600): used by your application.
08-08 15:03:35.743: E/mono-rt(1600): =================================================================

To reproduce this issue, please use the following test case:

Steps to reproduce:
Startup activity, click on the button to go to the second activity, click on the button go back to the startup activity and it crashes.

Versioning information:
Microsoft Visual Studio Professional 2012
Version 11.0.60610.01 Update 3
Microsoft .NET Framework
Version 4.5.50709

Installed Version: Professional

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Comment 2 Jonathan Pryor 2013-08-13 13:59:22 UTC
Kumpera: this appears to be a GC bug.

The cause for the crash is that within SecondActivity.clearCache(), `kvp.Value.Handle` is IntPtr.Zero, i.e. the Bitmap has been collected. This doesn't make sense to me, as (via additional logging) SecondActivity.Dispose(bool) isn't invoked and SecondActivity.Handle is not IntPtr.Zero, so I don't understand why the GC collected the Bitmap instances.

Changing SecondActivity.MemoryCache from a List<KeyValuePair<string, Bitmap>> to a List<Bitmap>has no effect (Bitmap.Handle is still IntPtr.Zero when clearCache() executes).
Comment 3 Jonathan Pryor 2013-08-13 14:05:28 UTC
Workaround: check the value of `kvp.Value.Handle` before invoking bm.IsRecycled:

  foreach (KeyValuePair<String, Bitmap> kvp in MemoryCache) {
      if (kvp.Value.Handle == IntPtr.Zero)
Comment 5 Brendan Zagaeski (Xamarin Team, assistant) 2013-09-17 18:19:15 UTC
Two more users have run into this:

1. Another case involving Bitmaps.

2. A case involving Views in MvvmCross/CrossUI.
Comment 10 Jonathan Pryor 2013-09-27 21:51:56 UTC
*** Bug 14188 has been marked as a duplicate of this bug. ***