[mono-android] Tracking GlobalReferences

[NebulaSleuth]

I have been working to find lost Global References in my application.  I have
been able to find and address just about everything, but I have some
questions about the information in the debug.mono.log data.

First I seem to get a recurring Global Reference allocation with the *same*
address, that never seems to be deallocated.  But the information doesn't
point me to anywhere that I can find in my code.  I was hoping someone had
an idea of what a NoClassDefError might be related to.  It seems to occur
shortly after each GC pass.  So I lose a global handle every ~30s or so. 

The handle is always the same: 0x4001518

--------------------------

I/monodroid-gref(18413): +g+ grefc 245 gwrefc 0 obj-handle 0x40015158/L ->
new-handle 0x40015158/L from    at
Java.Lang.Object.RegisterInstance(IJavaObject instance, IntPtr value,
JniHandleOwnership transfer)
I/monodroid-gref(18413):    at Java.Lang.Throwable.SetHandle(IntPtr value,
JniHandleOwnership transfer)
I/monodroid-gref(18413):    at Java.Lang.Throwable..ctor(IntPtr handle,
JniHandleOwnership transfer)
I/monodroid-gref(18413):    at Java.Lang.Error..ctor(IntPtr javaReference,
JniHandleOwnership transfer)
I/monodroid-gref(18413):    at Java.Lang.LinkageError..ctor(IntPtr
javaReference, JniHandleOwnership transfer)
I/monodroid-gref(18413):    at Java.Lang.NoClassDefFoundError..ctor(IntPtr
javaReference, JniHandleOwnership transfer)
I/monodroid-gref(18413):    at
System.Reflection.MonoCMethod.Invoke(System.Object obj, BindingFlags
invokeAttr, System.Reflection.Binder binder, System.Object[] parameters,
System.Globalization.CultureInfo culture)
I/monodroid-gref(18413):    at
System.Reflection.MonoCMethod.Invoke(BindingFlags invokeAttr,
System.Reflection.Binder binder, System.Object[] parameters,
System.Globalization.CultureInfo culture)
I/monodroid-gref(18413):    at
System.Reflection.ConstructorInfo.Invoke(System.Object[] p
I/monodroid-gref(18413): handle 0x40015158; key_handle 0x40015158: Java
Type: `java/lang/NoClassDefFoundError`; MCW type:
`Java.Lang.NoClassDefFoundError`

---------------------

Secondly, I have a recurring allocation that seems to be freed during GC,
but then gets 'resurrected' in a second phase.  It seems to be related to a
weak reference, but again it doesn't give me much to go on other than it
seems to be a string.

-----------------------
I/monodroid-gref(20680): +g+ grefc 288 gwrefc 0 obj-handle 0x405557a0/L ->
new-handle 0x405557a0/L from    at
Java.Lang.Object.RegisterInstance(IJavaObject instance, IntPtr value,
JniHandleOwnership transfer)
I/monodroid-gref(20680):    at Java.Lang.Object.SetHandle(IntPtr value,
JniHandleOwnership transfer)
I/monodroid-gref(20680):    at Java.Lang.Object..ctor(IntPtr handle,
JniHandleOwnership transfer)
I/monodroid-gref(20680):    at Java.Lang.String..ctor(IntPtr javaReference,
JniHandleOwnership transfer)
I/monodroid-gref(20680):    at
System.Reflection.MonoCMethod.Invoke(System.Object obj, BindingFlags
invokeAttr, System.Reflection.Binder binder, System.Object[] parameters,
System.Globalization.CultureInfo culture)
I/monodroid-gref(20680):    at
System.Reflection.MonoCMethod.Invoke(BindingFlags invokeAttr,
System.Reflection.Binder binder, System.Object[] parameters,
System.Globalization.CultureInfo culture)
I/monodroid-gref(20680):    at
System.Reflection.ConstructorInfo.Invoke(System.Object[] parameters)
I/monodroid-gref(20680):    at
Android.Runtime.TypeManager.CreateProxy(System.Type type, IntPtr handle,
JniHandleOwnership transfer)
I/monodroid-gref(20680):    at
Android.Runtime.TypeManager.CreateInstance(IntPtr handle, Jn
I/monodroid-gref(20680): handle 0x405557a0; key_handle 0x405557a0: Java
Type: `java/lang/String`; MCW type: `Java.Lang.String`

...

I/monodroid-gref(20680): -g- grefc 267 gwrefc 23 handle 0x40553428/G from
take_weak_global_ref_jni
I/monodroid-gref(20680): *take_weak obj=0x51503cb0 -> wref=0xde5a99d7
handle=0x405557a0
I/monodroid-gref(20680): +w+ grefc 267 gwrefc 24 obj-handle 0x405557a0/G ->
new-handle 0xde5a99d7/W from take_weak_global_ref_jni
...

I/monodroid-gref(20680): *try_take_global obj=0x51503cb0 -> wref=0xde5a99d7
handle=0x405557a0
I/monodroid-gref(20680): +g+ grefc 248 gwrefc 24 obj-handle 0xde5a99d7/W ->
new-handle 0x405557a0/G from take_global_ref_jni
I/monodroid-gref(20680): -w- grefc 248 gwrefc 23 handle 0xde5a99d7/W from
take_global_ref_jni
-----------------------


I am concerned about both of these since the total reference count seems to
continue to go up on each of these, but never goes back down (at least when
running for hours).

------------------------------

I have written a tool that I have been using to help track the GRefs.  You
can download a copy  http://www.extrastrength.com/files/GRefMonitor.exe here 

Hopefully, someone will find it useful.

-Mike



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