[CoreCLR/NativeAOT] Use a no-GC region during Android startup

src/Mono.Android/Android.App/Activity.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Diagnostics.CodeAnalysis;
+using System.Runtime.Versioning;
 using Android.Runtime;
 
 namespace Android.App {
@@ -39,7 +40,40 @@ public void RunOnUiThread (Action action)
 		{
 			RunOnUiThread (new Java.Lang.Thread.RunnableImplementor (action));
 		}
-	}
-}
 
+		[SupportedOSPlatform ("android19.0")]
+		[Register ("reportFullyDrawn", "()V", "GetReportFullyDrawnHandler")]
+		public virtual unsafe void ReportFullyDrawn ()
+		{
+			const string id = "reportFullyDrawn.()V";
+			try {
+				_members.InstanceMethods.InvokeVirtualVoidMethod (id, this, null);
+			} finally {
+				StartupNoGCRegion.End ();
+			}
+		}
+
+		static Delegate? cb_reportFullyDrawn_ReportFullyDrawn_V;
+
+		static Delegate GetReportFullyDrawnHandler ()
+		{
+			return cb_reportFullyDrawn_ReportFullyDrawn_V ??= new _JniMarshal_PP_V (n_ReportFullyDrawn);
+		}
+
+		static void n_ReportFullyDrawn (IntPtr jnienv, IntPtr native__this)
+		{
+			unsafe {
+				Java.Interop.JniMarshal.SafeInvokeAction (jnienv, native__this, &__n_ReportFullyDrawn);
+			}
+		}
 
+		static void __n_ReportFullyDrawn (IntPtr jnienv, IntPtr native__this)
+		{
+			var activity = Java.Lang.Object.GetObject<Activity> (jnienv, native__this, JniHandleOwnership.DoNotTransfer);
+			if (activity == null) {
+				throw new InvalidOperationException ("Could not obtain the managed Activity instance for reportFullyDrawn.");
+			}
+			activity.ReportFullyDrawn ();
+		}
+	}
+}

src/Mono.Android/Android.Runtime/JNIEnvInit.cs

@@ -109,6 +109,7 @@ internal static void InitializeNativeAotRuntime (JniRuntime runtime, JnienvIniti
 				throw new NotSupportedException ("Internal error: NativeAOT cannot be enabled with MonoVM or CoreCLR.");
 			}
 
+			StartupNoGCRegion.Start ();
 			androidRuntime = runtime;
 			JniRuntime.SetCurrent (runtime);
 			RegisterTrimmableTypeMapNativeMethodsIfNeeded ();
@@ -126,6 +127,8 @@ internal static unsafe void Initialize (JnienvInitializeArgs* args)
 				throw new NotSupportedException ("Internal error: exactly one of RuntimeFeature.IsMonoRuntime or RuntimeFeature.IsCoreClrRuntime must be enabled.");
 			}
 
+			StartupNoGCRegion.Start ();
+
 			IntPtr total_timing_sequence = IntPtr.Zero;
 			IntPtr partial_timing_sequence = IntPtr.Zero;
 

src/Mono.Android/Android.Runtime/StartupNoGCRegion.cs

@@ -0,0 +1,88 @@
+using System;
+using System.Threading;
+
+namespace Android.Runtime;
+
+sealed class StartupNoGCRegion
+{
+	const long Budget = 24 * 1024 * 1024;
+	// Bound the process-wide region when an app never reports that startup is fully drawn.
+	static readonly TimeSpan DefaultFallbackTimeout = TimeSpan.FromSeconds (10);
+	static readonly StartupNoGCRegion instance = new ();
+
+	readonly Lock sync = new ();
+	Timer? fallbackTimer;
+	State state;
+
+	enum State
+	{
+		NotStarted,
+		Active,
+		Ended,
+	}
+
+	internal static void Start () => instance.StartRegion ();
+
+	internal static void End () => instance.Finish ();
+
+	void StartRegion ()
+	{
+		if (Microsoft.Android.Runtime.RuntimeFeature.IsMonoRuntime) {
+			return;
+		}
+
+		lock (sync) {
+			if (state != State.NotStarted) {
+				return;
+			}
+
+			bool started;
+			try {
+				started = GC.TryStartNoGCRegion (Budget, disallowFullBlockingGC: true);
+			} catch (InvalidOperationException) {
+				state = State.Ended;
+				return;
+			}
+
+			if (!started) {
+				state = State.Ended;
+				return;
+			}
+
+			fallbackTimer = new Timer (
+				static value => {
+					if (value is StartupNoGCRegion noGCRegion) {
+						noGCRegion.Finish ();
+					}
+				},
+				this,
+				DefaultFallbackTimeout,
+				Timeout.InfiniteTimeSpan
+			);
+			state = State.Active;
+		}
+	}
+
+	void Finish ()
+	{
+		Timer? timer;
+		lock (sync) {
+			if (state != State.Active) {
+				return;
+			}
+
+			state = State.Ended;
+			timer = fallbackTimer;
+			fallbackTimer = null;
+		}
+
+		timer?.Dispose ();
+
+		try {
+			GC.EndNoGCRegion ();
+		} catch (InvalidOperationException) {
+			// The runtime already left the region because its budget was exhausted
+			// or a collection was induced.
+		}
+	}
+}

src/Mono.Android/Mono.Android.csproj

@@ -269,6 +269,7 @@
     <Compile Include="Android.Runtime\RuntimeConstants.cs" />
     <Compile Include="Android.Runtime\ResourceIdManager.cs" />
     <Compile Include="Android.Runtime\RuntimeNativeMethods.cs" />
+    <Compile Include="Android.Runtime\StartupNoGCRegion.cs" />
     <Compile Include="Android.Runtime\StringDefAttribute.cs" />
     <Compile Include="Android.Runtime\TimingLogger.cs" />
     <Compile Include="Android.Runtime\TypeManager.cs" />

src/Mono.Android/metadata

@@ -158,6 +158,7 @@
   <attr api-since="11" path="/api/package[@name='android.animation']/interface[@name='TypeEvaluator']/method[@name='evaluate']/parameter[@name='endValue']" name="type">java.lang.Object</attr>
   <attr path="/api/package[@name='android.accessibilityservice']" name="managedName">Android.AccessibilityServices</attr>
   <attr api-since="11" path="/api/package[@name='android.app']/class[@name='ActionBar.LayoutParams']/field[@name='gravity']" name="type">Android.Views.GravityFlags</attr>
+  <remove-node path="/api/package[@name='android.app']/class[@name='Activity']/method[@name='reportFullyDrawn']" />
   <attr path="/api/package[@name='android.app']/class[@name='Dialog']/method[@name='setOnKeyListener']" name="eventName">KeyPress</attr>
   <attr path="/api/package[@name='android.app']/interface[@name='DatePickerDialog.OnDateSetListener']/method[@name='onDateSet']/parameter[@name='view']" name="sender">true</attr>
   <attr path="/api/package[@name='android.app']/interface[@name='TimePickerDialog.OnTimeSetListener']/method[@name='onTimeSet']/parameter[@name='view']" name="sender">true</attr>