[android] interpreter does not run Java/C# object finalizers in some cases

[jonathanpeppers]

Description

This started happening here: dotnet/android#6363 (comment)

We think this diff: 491ed9a...e013f14

A test of the form:

var d = false;
var f = false;
FinalizerHelpers.PerformNoPinAction (() => {
    var v     = new JavaDisposedObject (() => d = true, () => f = true);
    GC.KeepAlive (v);
});
JniEnvironment.Runtime.ValueManager.CollectPeers ();
GC.WaitForPendingFinalizers ();
JniEnvironment.Runtime.ValueManager.CollectPeers ();
GC.WaitForPendingFinalizers ();
Assert (!d, "d should be false");
Assert (f, "f should be true");

Reproduction Steps

I created a self-contained repro: https://github.com/jonathanpeppers/net6-finalizer-repro

The interesting bit, is I don't even have to set UseInterpreter=true. The repro fails with JIT and interpreter.

Expected behavior

The above unit test passes.

Actual behavior

The above unit test fails.

Regression?

Yes, this has been working in Xamarin.Android for some time.

It worked previously in the 6.0.0-rtm.21472.13 version of the Mono/Android runtime packs.

Known Workarounds

Use older runtime packs?

<Target Name="UpdateMonoRuntimePacks" BeforeTargets="ProcessFrameworkReferences">
  <ItemGroup>
    <KnownRuntimePack 
        Update="Microsoft.NETCore.App"
        Condition=" '%(KnownRuntimePack.TargetFramework)' == 'net6.0' "
        LatestRuntimeFrameworkVersion="6.0.0-rtm.21472.13"
    />
  </ItemGroup>
</Target>

Configuration

.NET 6.0.100-rtm.21518.6

Other information

No response

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[jonathanpeppers]

/cc @BrzVlad @steveisok

Tagging subscribers to this area: @BrzVlad
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

This started happening here: dotnet/android#6363 (comment)

We think this diff: 491ed9a...e013f14

A test of the form:

var d = false;
var f = false;
FinalizerHelpers.PerformNoPinAction (() => {
    var v     = new JavaDisposedObject (() => d = true, () => f = true);
    GC.KeepAlive (v);
});
JniEnvironment.Runtime.ValueManager.CollectPeers ();
GC.WaitForPendingFinalizers ();
JniEnvironment.Runtime.ValueManager.CollectPeers ();
GC.WaitForPendingFinalizers ();
Assert (!d, "d should be false");
Assert (f, "f should be true");

Reproduction Steps

I created a self-contained repro: https://github.com/jonathanpeppers/net6-finalizer-repro

The interesting bit, is I don't even have to set UseInterpreter=true. The repro fails with JIT and interpreter.

Expected behavior

The above unit test passes.

Actual behavior

The above unit test fails.

Regression?

Yes, this has been working in Xamarin.Android for some time.

It worked previously in the 6.0.0-rtm.21472.13 version of the Mono/Android runtime packs.

Known Workarounds

Use older runtime packs?

<Target Name="UpdateMonoRuntimePacks" BeforeTargets="ProcessFrameworkReferences">
  <ItemGroup>
    <KnownRuntimePack 
        Update="Microsoft.NETCore.App"
        Condition=" '%(KnownRuntimePack.TargetFramework)' == 'net6.0' "
        LatestRuntimeFrameworkVersion="6.0.0-rtm.21472.13"
    />
  </ItemGroup>
</Target>

Configuration

.NET 6.0.100-rtm.21518.6

Other information

No response

Author:	jonathanpeppers
Assignees:	-
Labels:	untriaged, area-GC-mono
Milestone:	-

[BrzVlad]

As expected, this is not really a bug, but some weird pinning case. Was wondering why on android there are two collections being triggered, when I expected one to be enough. The reason the test case is not working is that the object to be collected is a bridge object. This means that, during the first collection the object is still kept alive by java side. The collection will store this obj ref on the main thread stack and this ref gets the object pinned during second collection.

In order to workaround this pinning issue, the test case can be rewritten as such :

var d = false;
var f = false;
FinalizerHelpers.PerformNoPinAction (() => {
    FinalizerHelpers.PerformNoPinAction (() => {
        var v     = new JavaDisposedObject (() => d = true, () => f = true);
        GC.KeepAlive (v);
    });
    JniEnvironment.Runtime.ValueManager.CollectPeers ();
});
JniEnvironment.Runtime.ValueManager.CollectPeers ();
GC.WaitForPendingFinalizers ();
Assert (!d, "d should be false");
Assert (f, "f should be true");

[jonathanpeppers]

Thanks, testing this out here:

• [tests] rework JavaObjectTest, use FinalizerHelper from mono/mono java-interop#899
• Testing: https://github.com/xamarin/java.interop/pull/899 android#6418