[Mono.Android] call new Java "GC Bridge" APIs

Context: dotnet/runtime#114184
Context: https://github.com/jonathanpeppers/BridgeSandbox
Context: dotnet/runtime@main...BrzVlad:runtime:feature-clr-gcbridge

So far, I:

* Built dotnet/runtime, I built this branch:

https://github.com/jonathanpeppers/runtime/tree/gcbridge_impl

* Put the relevant arm64 packs in `packages/` folder and configured a
  `NuGet.config` to use them.

* Setup `build-tools\scripts\custom-runtime.targets` to use the
  10.0.0-dev dotnet/runtime packs.

* In `ManagedValueManager.cs`...

* Call a new native method on startup:

    var mark_cross_references_ftn = RuntimeNativeMethods.clr_initialize_gc_bridge (&BridgeProcessingFinished);

* Pass the returned function pointer to:

    JavaMarshal.Initialize (mark_cross_references_ftn);

* In `AddPeer(IJavaPeerable value)` call `JavaMarshal.CreateReferenceTrackingHandle()`

* In `RemovePeer(IJavaPeerable value)` call:

    static unsafe void FreeHandle (GCHandle handle)
    {
        IntPtr context = JavaMarshal.GetContext (handle);
        NativeMemory.Free((void*)context);
    }

Author: jonathanpeppers

.gitattributes

@@ -35,3 +35,5 @@ Makefile	eol=lf
 *.wixproj	eol=crlf
 *.wxs	eol=crlf
 *.rtf	eol=crlf
+
+packages/* filter=lfs diff=lfs merge=lfs -text

Documentation/workflow/DevelopmentTips.md

@@ -450,13 +450,26 @@ A second (better) way is to add this MSBuild target to your Android
 `.csproj` file:
 
 ```xml
-<Target Name="UpdateMonoRuntimePacks" BeforeTargets="ProcessFrameworkReferences">
+<Target Name="UpdateRuntimeVersion" BeforeTargets="ProcessFrameworkReferences">
+  <PropertyGroup>
+    <!-- This could be a version I built myself -->
+    <_Version>10.0.0-dev</_Version>
+  </PropertyGroup>
   <ItemGroup>
-      <KnownRuntimePack
-          Update="Microsoft.NETCore.App"
-          Condition=" '%(KnownRuntimePack.TargetFramework)' == 'net6.0' "
-          LatestRuntimeFrameworkVersion="6.0.0-preview.7.21364.3"
-      />
+    <!-- For runtime packs only -->
+    <KnownRuntimePack
+        Update="Microsoft.NETCore.App"
+        Condition=" '%(KnownRuntimePack.TargetFramework)' == 'net10.0' "
+        LatestRuntimeFrameworkVersion="$(_Version)"
+    />
+    <!-- For new .NET APIs -->
+    <KnownFrameworkReference
+        Update="Microsoft.NETCore.App"
+        Condition=" '%(KnownFrameworkReference.TargetFramework)' == 'net10.0' "
+        DefaultRuntimeFrameworkVersion="$(_Version)"
+        LatestRuntimeFrameworkVersion="$(_Version)"
+        TargetingPackVersion="$(_Version)"
+    />
   </ItemGroup>
 </Target>
 ```

NuGet.config

@@ -7,6 +7,7 @@
     <!--  End: Package sources from dotnet-android -->
     <!--End: Package sources managed by Dependency Flow automation. Do not edit the sources above.-->
     <!-- ensure only the sources defined below are used -->
+    <add key="local-packages" value="packages" />
     <add key="dotnet-public" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public/nuget/v3/index.json" protocolVersion="3" />
     <add key="dotnet-eng" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-eng/nuget/v3/index.json" protocolVersion="3" />
     <!-- This is for packages needed by debugger-libs -->

build-tools/scripts/custom-runtime.targets

@@ -0,0 +1,21 @@
+<Project>
+  <!-- Use version in local packages folder -->
+  <Target Name="UpdateRuntimeVersion" BeforeTargets="ProcessFrameworkReferences">
+    <PropertyGroup>
+      <_Version>10.0.0-dev</_Version>
+    </PropertyGroup>
+    <ItemGroup>
+        <KnownFrameworkReference Update="Microsoft.NETCore.App"
+            Condition=" '%(KnownFrameworkReference.TargetFramework)' == 'net10.0' "
+            DefaultRuntimeFrameworkVersion="$(_Version)"
+            LatestRuntimeFrameworkVersion="$(_Version)"
+            TargetingPackVersion="$(_Version)"
+        />
+        <KnownRuntimePack
+            Update="Microsoft.NETCore.App"
+            Condition=" '%(KnownRuntimePack.TargetFramework)' == 'net10.0' "
+            LatestRuntimeFrameworkVersion="$(_Version)"
+        />
+    </ItemGroup>
+  </Target>
+</Project>

packages/Microsoft.NETCore.App.Ref.10.0.0-dev.nupkg

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:d23f78cb9dec82f9ed64e0b9b803fe533d2628d63e1af54685ff8827b1d799bb
+size 5313525

packages/Microsoft.NETCore.App.Runtime.android-arm64.10.0.0-dev.nupkg

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:7c6e9746aaf2b91c7009d940eeda588129f4be8fc864ca6259dc6e5845abe48f
+size 215347082

src/Mono.Android.Runtime/Mono.Android.Runtime.csproj

@@ -64,5 +64,6 @@
     <ProjectReference Include="..\..\external\Java.Interop\src\Java.Interop\Java.Interop.csproj" />
   </ItemGroup>
 
+  <Import Project="..\..\build-tools\scripts\custom-runtime.targets" />
   <Import Project="Mono.Android.Runtime.targets" />
 </Project>

src/Mono.Android/Android.Runtime/RuntimeNativeMethods.cs

@@ -2,6 +2,7 @@
 using System;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
+using System.Runtime.InteropServices.Java;
 using System.Text;
 
 namespace Android.Runtime
@@ -18,7 +19,7 @@ enum TraceKind : uint
 		All     = Java | Managed | Native | Signals,
 	}
 
-	internal static class RuntimeNativeMethods
+	internal unsafe static class RuntimeNativeMethods
 	{
 		[DllImport (RuntimeConstants.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		internal extern static void monodroid_log (LogLevel level, LogCategories category, string message);
@@ -92,6 +93,17 @@ internal static class RuntimeNativeMethods
 		[DllImport (RuntimeConstants.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		internal static extern bool clr_typemap_java_to_managed (string java_type_name, out IntPtr managed_assembly_name, out uint managed_type_token_id);
 
+		/// <summary>
+		/// TODO: implement this in the native side.
+		/// Initializes the "GC Bridge" implementation for the CoreCLR runtime.
+		/// </summary>
+		/// <param name="bridge_processing_finished_callback">A function pointer to a C# callback that will be invoked when bridge processing has completed.</param>
+		/// <returns>A function pointer that should be passed to JavaMarshal.Initialize() on startup.</returns>
+		[DllImport (RuntimeConstants.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
+		internal static extern delegate* unmanaged<nint, StronglyConnectedComponent*, nint, ComponentCrossReference*, void> clr_initialize_gc_bridge (
+			delegate* unmanaged<nint, StronglyConnectedComponent*, nint, ComponentCrossReference*, void> bridge_processing_finished_callback
+		);
+
 		[MethodImplAttribute(MethodImplOptions.InternalCall)]
 		internal static extern void monodroid_unhandled_exception (Exception javaException);
 

src/Mono.Android/Microsoft.Android.Runtime/ManagedValueManager.cs

@@ -10,6 +10,7 @@
 using System.Reflection;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
+using System.Runtime.InteropServices.Java;
 using System.Threading;
 using Android.Runtime;
 using Java.Interop;
@@ -20,10 +21,12 @@ class ManagedValueManager : JniRuntime.JniValueManager
 {
 	const DynamicallyAccessedMemberTypes Constructors = DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors;
 
-	Dictionary<int, List<IJavaPeerable>>?   RegisteredInstances = new Dictionary<int, List<IJavaPeerable>>();
+	Dictionary<int, List<GCHandle>>?   RegisteredInstances = new ();
 
-	internal ManagedValueManager ()
+	internal unsafe ManagedValueManager ()
 	{
+		var mark_cross_references_ftn = RuntimeNativeMethods.clr_initialize_gc_bridge (&BridgeProcessingFinished);
+		JavaMarshal.Initialize (mark_cross_references_ftn);
 	}
 
 	public override void WaitForGCBridgeProcessing ()
@@ -35,7 +38,7 @@ public override void CollectPeers ()
 		if (RegisteredInstances == null)
 			throw new ObjectDisposedException (nameof (ManagedValueManager));
 
-		var peers = new List<IJavaPeerable> ();
+		var peers = new List<GCHandle> ();
 
 		lock (RegisteredInstances) {
 			foreach (var ps in RegisteredInstances.Values) {
@@ -48,7 +51,8 @@ public override void CollectPeers ()
 		List<Exception>? exceptions = null;
 		foreach (var peer in peers) {
 			try {
-				peer.Dispose ();
+				if (peer.Target is IDisposable disposable)
+					disposable.Dispose ();
 			}
 			catch (Exception e) {
 				exceptions = exceptions ?? new List<Exception> ();
@@ -74,33 +78,35 @@ public override void AddPeer (IJavaPeerable value)
 		}
 		int key = value.JniIdentityHashCode;
 		lock (RegisteredInstances) {
-			List<IJavaPeerable>? peers;
+			List<GCHandle>? peers;
 			if (!RegisteredInstances.TryGetValue (key, out peers)) {
-				peers = new List<IJavaPeerable> () {
-					value,
+				peers = new List<GCHandle> () {
+					CreateReferenceTrackingHandle (value)
 				};
 				RegisteredInstances.Add (key, peers);
 				return;
 			}
 
 			for (int i = peers.Count - 1; i >= 0; i--) {
 				var p   = peers [i];
-				if (!JniEnvironment.Types.IsSameObject (p.PeerReference, value.PeerReference))
+				if (p.Target is not IJavaPeerable peer)
+					continue;
+				if (!JniEnvironment.Types.IsSameObject (peer.PeerReference, value.PeerReference))
 					continue;
 				if (Replaceable (p)) {
-					peers [i] = value;
+					peers [i] = CreateReferenceTrackingHandle (value);
 				} else {
-					WarnNotReplacing (key, value, p);
+					WarnNotReplacing (key, value, peer);
 				}
 				return;
 			}
-			peers.Add (value);
+			peers.Add (CreateReferenceTrackingHandle (value));
 		}
 	}
 
-	static bool Replaceable (IJavaPeerable peer)
+	static bool Replaceable (GCHandle handle)
 	{
-		if (peer == null)
+		if (handle.Target is not IJavaPeerable peer)
 			return true;
 		return peer.JniManagedPeerState.HasFlag (JniManagedPeerStates.Replaceable);
 	}
@@ -132,14 +138,14 @@ void WarnNotReplacing (int key, IJavaPeerable ignoreValue, IJavaPeerable keepVal
 		int key = GetJniIdentityHashCode (reference);
 
 		lock (RegisteredInstances) {
-			List<IJavaPeerable>? peers;
+			List<GCHandle>? peers;
 			if (!RegisteredInstances.TryGetValue (key, out peers))
 				return null;
 
 			for (int i = peers.Count - 1; i >= 0; i--) {
 				var p = peers [i];
-				if (JniEnvironment.Types.IsSameObject (reference, p.PeerReference))
-					return p;
+				if (p.Target is IJavaPeerable peer && JniEnvironment.Types.IsSameObject (reference, peer.PeerReference))
+					return peer;
 			}
 			if (peers.Count == 0)
 				RegisteredInstances.Remove (key);
@@ -157,14 +163,15 @@ public override void RemovePeer (IJavaPeerable value)
 
 		int key = value.JniIdentityHashCode;
 		lock (RegisteredInstances) {
-			List<IJavaPeerable>? peers;
+			List<GCHandle>? peers;
 			if (!RegisteredInstances.TryGetValue (key, out peers))
 				return;
 
 			for (int i = peers.Count - 1; i >= 0; i--) {
 				var p   = peers [i];
-				if (object.ReferenceEquals (value, p)) {
+				if (object.ReferenceEquals (value, p.Target)) {
 					peers.RemoveAt (i);
+					FreeHandle (p);
 				}
 			}
 			if (peers.Count == 0)
@@ -251,13 +258,32 @@ public override List<JniSurfacedPeerInfo> GetSurfacedPeers ()
 			var peers = new List<JniSurfacedPeerInfo> (RegisteredInstances.Count);
 			foreach (var e in RegisteredInstances) {
 				foreach (var p in e.Value) {
-					peers.Add (new JniSurfacedPeerInfo (e.Key, new WeakReference<IJavaPeerable> (p)));
+					if (p.Target is not IJavaPeerable peer)
+						continue;
+					peers.Add (new JniSurfacedPeerInfo (e.Key, new WeakReference<IJavaPeerable> (peer)));
 				}
 			}
 			return peers;
 		}
 	}
 
+	static GCHandle CreateReferenceTrackingHandle (IJavaPeerable value) =>
+		JavaMarshal.CreateReferenceTrackingHandle (value, value.PeerReference.Handle);
+		
+	static unsafe void FreeHandle (GCHandle handle)
+	{
+		IntPtr context = JavaMarshal.GetContext (handle);
+		NativeMemory.Free ((void*) context);
+	}
+	
+	[UnmanagedCallersOnly]
+	internal static unsafe void BridgeProcessingFinished (nint sccsLen, StronglyConnectedComponent* sccs, nint ccrsLen, ComponentCrossReference* ccrs)
+	{
+		JavaMarshal.ReleaseMarkCrossReferenceResources (
+			new Span<StronglyConnectedComponent> (sccs, (int) sccsLen),
+			new Span<ComponentCrossReference> (ccrs, (int) ccrsLen));
+	}
+
 	const   BindingFlags    ActivationConstructorBindingFlags   = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance;
 
 	static  readonly    Type[]  XAConstructorSignature  = new Type [] { typeof (IntPtr), typeof (JniHandleOwnership) };

src/Mono.Android/Mono.Android.csproj

@@ -113,6 +113,7 @@
   <Import Project="..\Xamarin.Android.NamingCustomAttributes\Xamarin.Android.NamingCustomAttributes.projitems" Label="Shared" Condition="Exists('..\Xamarin.Android.NamingCustomAttributes\Xamarin.Android.NamingCustomAttributes.projitems')" />
   <Import Project="Mono.Android.targets" />
   <Import Project="..\..\build-tools\scripts\JavaCallableWrappers.targets" />
+  <Import Project="..\..\build-tools\scripts\custom-runtime.targets" />
   <Import Project="$(IntermediateOutputPath)mcw\Mono.Android.projitems" Condition="Exists('$(IntermediateOutputPath)mcw\Mono.Android.projitems')" />
 
 <ItemGroup>

src/native/clr/host/generate-pinvoke-tables.cc

@@ -72,6 +72,7 @@ const std::vector<std::string> internal_pinvoke_names = {
 	"monodroid_TypeManager_get_java_class_name",
 	"clr_typemap_managed_to_java",
 	"clr_typemap_java_to_managed",
+	"clr_initialize_gc_bridge",
 	"_monodroid_weak_gref_delete",
 	"_monodroid_weak_gref_get",
 	"_monodroid_weak_gref_new",

src/native/clr/host/internal-pinvokes.cc

@@ -36,6 +36,16 @@ bool clr_typemap_java_to_managed (const char *java_type_name, char const** assem
 	return TypeMapper::typemap_java_to_managed (java_type_name, assembly_name, managed_type_token_id);
 }
 
+static void clr_mark_cross_references (size_t sccsLen, StronglyConnectedComponent* sccs, size_t ccrsLen, ComponentCrossReference* ccrs)
+{
+	// TODO: implement this
+}
+
+MarkCrossReferencesFtn clr_initialize_gc_bridge (MarkCrossReferencesFtn callback) noexcept
+{
+	return clr_mark_cross_references;
+}
+
 void monodroid_log (LogLevel level, LogCategories category, const char *message) noexcept
 {
 	switch (level) {

src/native/clr/include/runtime-base/internal-pinvokes.hh

@@ -7,13 +7,28 @@
 #include "logger.hh"
 #include <runtime-base/timing.hh>
 
+struct StronglyConnectedComponent
+{
+    size_t Count;
+    void** ContextMemory;
+};
+
+struct ComponentCrossReference
+{
+    size_t SourceGroupIndex;
+    size_t DestinationGroupIndex;
+};
+
+typedef void (*MarkCrossReferencesFtn)(size_t, StronglyConnectedComponent*, size_t, ComponentCrossReference*);
+
 extern "C" {
 	int _monodroid_gref_get () noexcept;
 	void _monodroid_gref_log (const char *message) noexcept;
 	int _monodroid_gref_log_new (jobject curHandle, char curType, jobject newHandle, char newType, const char *threadName, int threadId, const char *from, int from_writable) noexcept;
 	void _monodroid_gref_log_delete (jobject handle, char type, const char *threadName, int threadId, const char *from, int from_writable) noexcept;
 	const char* clr_typemap_managed_to_java (const char *typeName, const uint8_t *mvid) noexcept;
 	bool clr_typemap_java_to_managed (const char *java_type_name, char const** assembly_name, uint32_t *managed_type_token_id) noexcept;
+	MarkCrossReferencesFtn clr_initialize_gc_bridge (MarkCrossReferencesFtn callback) noexcept;
 	void monodroid_log (xamarin::android::LogLevel level, LogCategories category, const char *message) noexcept;
 	char* monodroid_TypeManager_get_java_class_name (jclass klass) noexcept;
 	void monodroid_free (void *ptr) noexcept;