How to take heap snapshot of Xamarin.Android's Mono VM?

Question

Background: I am trying to track down a memory leak in a Xamarin.Android app. Using DDMS and Eclipse Memory Profiler, I am able to see which objects are alive. When trying to track what is holding them alive (GC Root), I only see "Native stack" (of course).

How can I take a heap snapshot of the MONO VM? So I can later use it with i.e. heapshot tool?

Or are there ANY OTHER TECHNIQUES I can use to find what is holding an object alive in Xamarin.Android's .NET part? Is it possible to do something from within the program?

Answer 1

How can I take a heap snapshot of the MONO VM? So I can later use it with i.e. heapshot tool?

It is now possible to get heap snapshots of the Mono VM (tested with Xamarin.Android 4.8.2 beta; may apply to prior releases, your mileage may vary). It's a four step process:

1. Enable heapshot logging:

   adb shell setprop debug.mono.profile log:heapshot
   

2. Start your app. (If your app was already running before (1), kill and restart it.)

   Use your app.

3. Grab the profile data for your app:

   adb pull /data/data/@PACKAGE_NAME@/files/.__override__/profile.mlpd
   

   @PACKAGE_NAME@ is the package name of your application, e.g. if your package is FooBar.FooBar-Signed.apk, then @PACKAGE_NAME@ will be FooBar.FooBar.

4. Analyze the data:

   mprof-report profile.mlpd
   

   mprof-report is included with Mono.

Note: profile.mlpd is only updated when a GC occurs, so you may want to call GC.Collect() at some "well known" point to ensure that profile.mlpd is regularly updated .