[flaky-ci] Isolate TryFindClass JNI leak checks

build-tools/automation/yaml-templates/stage-package-tests.yaml

@@ -155,6 +155,17 @@ stages:
 
     - template: /build-tools/automation/yaml-templates/start-stop-emulator.yaml
 
+    # Process-wide JNI reference counts need a fresh process without unrelated tests.
+    - template: /build-tools/automation/yaml-templates/apk-instrumentation.yaml
+      parameters:
+        buildConfiguration: $(XA.Build.Configuration)
+        configuration: Debug
+        testName: Mono.Android.NET_Tests-JniReferenceLeaks
+        project: tests/Mono.Android-Tests/Mono.Android-Tests/Mono.Android.NET-Tests.csproj
+        extraBuildArgs: -p:TestsFlavor=JniReferenceLeaks -p:IncludeCategories=JniReferenceLeak -p:UseMonoRuntime=false
+        artifactSource: bin/TestDebug/$(DotNetTargetFramework)-android/Mono.Android.NET_Tests-Signed.apk
+        artifactFolder: $(DotNetTargetFramework)-JniReferenceLeaks
+
     # Smoke coverage that the test app still builds and runs under Mono.
     - template: /build-tools/automation/yaml-templates/apk-instrumentation.yaml
       parameters:

external/Java.Interop/tests/Java.Interop-Tests/Java.Interop/JniTypeUtf8Test.cs

@@ -1,6 +1,7 @@
 #nullable enable
 
 using System;
+using System.Collections.Generic;
 
 using Java.Interop;
 
@@ -11,6 +12,9 @@ namespace Java.InteropTests
 	[TestFixture]
 	public class JniTypeUtf8Test : JavaVMFixture {
 
+		const string JniReferenceLeakCategory = "JniReferenceLeak";
+		const int LeakCheckIterations = 100;
+
 		[Test]
 		public unsafe void Sanity_Utf8 ()
 		{
@@ -91,24 +95,77 @@ public void TryFindClass_Utf8 ()
 		}
 
 		[Test]
-		[Ignore ("Frequently failing: https://github.com/dotnet/android/issues/12031")]
+		[Category (JniReferenceLeakCategory)]
 		public void TryFindClass_Utf8_DoesNotLeakGlobalRefs ()
 		{
-			int grefsBefore = JniEnvironment.Runtime.GlobalReferenceCount;
-			JniEnvironment.Types.TryFindClass ("does/not/Exist"u8, out _);
-			int grefsAfter = JniEnvironment.Runtime.GlobalReferenceCount;
-			Assert.AreEqual (grefsBefore, grefsAfter,
-				"TryFindClass for non-existent classes should not leak global references");
+			AssertNoSustainedGlobalReferenceGrowth (() => {
+				Assert.IsFalse (JniEnvironment.Types.TryFindClass ("does/not/Exist"u8, out var notFound));
+				Assert.IsFalse (notFound.IsValid);
+			});
 		}
 
 		[Test]
+		[Category (JniReferenceLeakCategory)]
 		public void TryFindClass_String_DoesNotLeakGlobalRefs ()
 		{
+			AssertNoSustainedGlobalReferenceGrowth (() => {
+				Assert.IsFalse (JniEnvironment.Types.TryFindClass ("does/not/Exist", out var notFound));
+				Assert.IsFalse (notFound.IsValid);
+			});
+		}
+
+		[Test]
+		[Category (JniReferenceLeakCategory)]
+		public void AssertNoSustainedGlobalReferenceGrowth_DetectsRetainedGlobalReference ()
+		{
+			var objectClass = JniEnvironment.Types.FindClass ("java/lang/Object");
+			var retainedReferences = new List<JniObjectReference> ();
+			try {
+				Assert.Throws<AssertionException> (() => AssertNoSustainedGlobalReferenceGrowth (() => {
+					retainedReferences.Add (objectClass.NewGlobalRef ());
+				}));
+			} finally {
+				foreach (var retainedReference in retainedReferences) {
+					var reference = retainedReference;
+					JniObjectReference.Dispose (ref reference);
+				}
+				JniObjectReference.Dispose (ref objectClass);
+			}
+		}
+
+		static void AssertNoSustainedGlobalReferenceGrowth (Action action)
+		{
+			for (int i = 0; i < LeakCheckIterations; i++) {
+				action ();
+			}
+			CollectPeers ();
+
 			int grefsBefore = JniEnvironment.Runtime.GlobalReferenceCount;
-			JniEnvironment.Types.TryFindClass ("does/not/Exist", out _);
+			for (int i = 0; i < LeakCheckIterations; i++) {
+				action ();
+			}
+			CollectGarbage ();
 			int grefsAfter = JniEnvironment.Runtime.GlobalReferenceCount;
-			Assert.AreEqual (grefsBefore, grefsAfter,
-				"TryFindClass for non-existent classes should not leak global references");
+
+			Assert.LessOrEqual (grefsAfter, grefsBefore,
+				$"Operation should not leak global references after {LeakCheckIterations} iterations. " +
+				$"Before={grefsBefore}, After={grefsAfter}, Delta={grefsAfter - grefsBefore}");
+		}
+
+		static void CollectPeers ()
+		{
+			CollectGarbage ();
+			JniEnvironment.Runtime.ValueManager.CollectPeers ();
+			JniEnvironment.Runtime.ValueManager.WaitForGCBridgeProcessing ();
+			CollectGarbage ();
+		}
+
+		static void CollectGarbage ()
+		{
+			for (int i = 0; i < 3; i++) {
+				GC.Collect ();
+				GC.WaitForPendingFinalizers ();
+			}
 		}
 
 		[Test]

tests/Mono.Android-Tests/Mono.Android-Tests/Xamarin.Android.RuntimeTests/TestInstrumentation.cs

@@ -11,6 +11,8 @@ namespace Xamarin.Android.RuntimeTests
 	[Instrumentation (Name = "xamarin.android.runtimetests.TestInstrumentation")]
 	public class TestInstrumentation : Xamarin.Android.UnitTests.TestInstrumentation
 	{
+		const string JniReferenceLeakCategory = "JniReferenceLeak";
+
 		protected TestInstrumentation (IntPtr handle, JniHandleOwnership transfer)
 			: base (handle, transfer)
 		{
@@ -54,6 +56,11 @@ protected override IEnumerable<string>? ExcludedCategories {
 					categories.Add ("NetworkInterfaces");
 				}
 
+				// Process-wide reference counts are only stable in the dedicated filtered run.
+				if (!IsOnlyIncludedCategory (JniReferenceLeakCategory)) {
+					categories.Add (JniReferenceLeakCategory);
+				}
+
 				return categories.Count > 0 ? categories : null;
 			}
 		}
@@ -66,13 +73,25 @@ protected override IEnumerable<string>? IncludedCategories {
 				// `configProperties` section, and we read it back with `AppContext.GetData`.
 				// Used by lanes that want to scope a run to specific categories, e.g.
 				// `-p:IncludeCategories=Intune` in stage-package-tests.yaml.
-				var value = AppContext.GetData ("IncludeCategories") as string;
-				if (string.IsNullOrEmpty (value))
-					return null;
-				return value!.Split (new [] { ',', ';' }, StringSplitOptions.RemoveEmptyEntries);
+				var categories = GetIncludedCategories ();
+				return categories.Length > 0 ? categories : null;
 			}
 		}
 
+		static bool IsOnlyIncludedCategory (string category)
+		{
+			var categories = GetIncludedCategories ();
+			return categories.Length == 1 && string.Equals (categories [0], category, StringComparison.Ordinal);
+		}
+
+		static string [] GetIncludedCategories ()
+		{
+			var value = AppContext.GetData ("IncludeCategories") as string;
+			if (value == null)
+				return [];
+			return value.Split (new [] { ',', ';' }, StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
+		}
+
 		static bool HasAppContextSwitch (string key)
 			=> AppContext.TryGetSwitch (key, out var value) && value;