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

Context: dotnet/runtime#114184
Context: https://github.com/jonathanpeppers/BridgeSandbox

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 a `UpdateRuntimePacks` target in the `Mono.Android.csproj` to
  use the 10.0.0-dev packs.

* Make use of the new `JavaMarshal.CreateReferenceTrackingHandle()` API

* This is WIP there are still more APIs.

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="UpdateKnownPacks" 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 -->

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/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;
@@ -20,7 +21,7 @@ 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 ()
 	{
@@ -35,7 +36,7 @@ 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 +49,8 @@ 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 +76,35 @@ 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> () {
+					JavaMarshal.CreateReferenceTrackingHandle (value, value.PeerReference.Handle)
 				};
 				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] = JavaMarshal.CreateReferenceTrackingHandle (value, value.PeerReference.Handle);
 				} else {
-					WarnNotReplacing (key, value, p);
+					WarnNotReplacing (key, value, peer);
 				}
 				return;
 			}
-			peers.Add (value);
+			peers.Add (JavaMarshal.CreateReferenceTrackingHandle (value, value.PeerReference.Handle));
 		}
 	}
 
-	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 +136,14 @@ 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);
@@ -157,13 +161,13 @@ 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);
 				}
 			}
@@ -251,7 +255,9 @@ 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;

src/Mono.Android/Mono.Android.csproj

@@ -25,6 +25,26 @@
     <ProduceReferenceAssembly>true</ProduceReferenceAssembly>
   </PropertyGroup>
 
+  <!-- Use version in local packages folder -->
+  <Target Name="UpdateRuntimePacks" 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>
+
   <PropertyGroup>
     <IsUnstableVersion Condition=" '$(AndroidApiLevel)' &gt; '$(AndroidLatestStableApiLevel)' ">true</IsUnstableVersion>
     <DefineConstants Condition=" '$(IsUnstableVersion)' == 'True' ">$(DefineConstants);ANDROID_UNSTABLE</DefineConstants>