Trigger Java GC directly through JNI from C# and remove unnecessary comment

- Call Runtime.gc() directly from C# via JNI instead of calling native code
- Remove clr_gc_bridge_trigger_java_gc P/Invoke and native implementation
- Remove unnecessary comment from host.cc line 66
- Simplify native GCBridge by removing Runtime instance caching
- Regenerate pinvoke-tables.include (now 24 internal p/invokes)

Co-authored-by: simonrozsival <374616+simonrozsival@users.noreply.github.com>

Author: Copilot

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

@@ -94,12 +94,6 @@ internal unsafe static class RuntimeNativeMethods
 		internal static extern delegate* unmanaged<MarkCrossReferencesArgs*, void> clr_gc_bridge_initialize_for_managed_processing (
 			delegate* unmanaged[Cdecl]<MarkCrossReferencesArgs*, void> onMarkCrossReferencesCallback);
 
-		/// <summary>
-		/// Trigger Java garbage collection.
-		/// </summary>
-		[DllImport (RuntimeConstants.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
-		internal static extern void clr_gc_bridge_trigger_java_gc ();
-
 		[MethodImplAttribute(MethodImplOptions.InternalCall)]
 		internal static extern void monodroid_unhandled_exception (Exception javaException);
 

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

@@ -29,6 +29,10 @@ unsafe class BridgeProcessing
 	static JniMethodInfo? s_GCUserPeerable_jiAddManagedReference;
 	static JniMethodInfo? s_GCUserPeerable_jiClearManagedReferences;
 
+	// For triggering Java GC directly
+	static JniObjectReference s_RuntimeInstance;
+	static JniMethodInfo? s_Runtime_gc;
+
 	// Is NativeAOT mode (uses GCUserPeerable instead of IGCUserPeer)
 	static bool s_initialized;
 	static bool s_isNativeAOT;
@@ -71,6 +75,14 @@ public static void Initialize (bool isNativeAOT)
 			s_GCUserPeerable_jiClearManagedReferences = s_GCUserPeerableClass.GetInstanceMethod ("jiClearManagedReferences", "()V");
 		}
 
+		// Initialize Java Runtime for triggering GC
+		using var runtimeClass = new JniType ("java/lang/Runtime");
+		var getRuntimeMethod = runtimeClass.GetStaticMethod ("getRuntime", "()Ljava/lang/Runtime;");
+		s_Runtime_gc = runtimeClass.GetInstanceMethod ("gc", "()V");
+		var runtimeLocal = JniEnvironment.StaticMethods.CallStaticObjectMethod (runtimeClass.PeerReference, getRuntimeMethod, null);
+		s_RuntimeInstance = runtimeLocal.NewGlobalRef ();
+		JniObjectReference.Dispose (ref runtimeLocal);
+
 		s_initialized = true;
 	}
 
@@ -262,11 +274,19 @@ bool TryCallGCUserPeerableAddManagedReference (JniObjectReference from, JniObjec
 	}
 
 	/// <summary>
-	/// Trigger Java garbage collection using the cached Runtime instance from native code.
+	/// Trigger Java garbage collection using the cached Runtime instance directly through JNI.
 	/// </summary>
 	static void TriggerJavaGC ()
 	{
-		RuntimeNativeMethods.clr_gc_bridge_trigger_java_gc ();
+		if (s_Runtime_gc == null) {
+			throw new InvalidOperationException ("BridgeProcessing.Initialize must be called before TriggerJavaGC");
+		}
+
+		try {
+			JniEnvironment.InstanceMethods.CallVoidMethod (s_RuntimeInstance, s_Runtime_gc, null);
+		} catch (Exception ex) {
+			Logger.Log (LogLevel.Error, "monodroid-gc", $"Java GC failed: {ex.Message}");
+		}
 	}
 
 	void TakeWeakGlobalRef (HandleContext* context)

src/native/clr/host/gc-bridge.cc

@@ -6,43 +6,13 @@
 
 using namespace xamarin::android;
 
-void GCBridge::initialize_on_onload (JNIEnv *env) noexcept
+void GCBridge::initialize_on_onload ([[maybe_unused]] JNIEnv *env) noexcept
 {
-	abort_if_invalid_pointer_argument (env, "env");
-
-	jclass Runtime_class = env->FindClass ("java/lang/Runtime");
-	abort_unless (Runtime_class != nullptr, "Failed to look up java/lang/Runtime class.");
-
-	jmethodID Runtime_getRuntime = env->GetStaticMethodID (Runtime_class, "getRuntime", "()Ljava/lang/Runtime;");
-	abort_unless (Runtime_getRuntime != nullptr, "Failed to look up the Runtime.getRuntime() method.");
-
-	Runtime_gc = env->GetMethodID (Runtime_class, "gc", "()V");
-	abort_unless (Runtime_gc != nullptr, "Failed to look up the Runtime.gc() method.");
-
-	Runtime_instance = OSBridge::lref_to_gref (env, env->CallStaticObjectMethod (Runtime_class, Runtime_getRuntime));
-	abort_unless (Runtime_instance != nullptr, "Failed to obtain Runtime instance.");
-
-	env->DeleteLocalRef (Runtime_class);
+	// Java Runtime.gc() is now called directly from managed code
 }
 
 void GCBridge::initialize_on_runtime_init ([[maybe_unused]] JNIEnv *env, [[maybe_unused]] jclass runtimeClass) noexcept
 {
-	// Bridge processing is now done in managed code (C#)
-	// No native initialization is needed
-}
-
-void GCBridge::trigger_java_gc (JNIEnv *env) noexcept
-{
-	abort_if_invalid_pointer_argument (env, "env");
-
-	env->CallVoidMethod (Runtime_instance, Runtime_gc);
-	if (!env->ExceptionCheck ()) [[likely]] {
-		return;
-	}
-
-	env->ExceptionDescribe ();
-	env->ExceptionClear ();
-	log_error (LOG_DEFAULT, "Java GC failed");
 }
 
 void GCBridge::mark_cross_references (MarkCrossReferencesArgs *args) noexcept

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

@@ -39,11 +39,6 @@ BridgeProcessingFtn clr_gc_bridge_initialize_for_managed_processing (OnMarkCross
 	return GCBridge::initialize_for_managed_processing (callback);
 }
 
-void clr_gc_bridge_trigger_java_gc () noexcept
-{
-	GCBridge::trigger_java_gc_cached ();
-}
-
 void monodroid_log (LogLevel level, LogCategories category, const char *message) noexcept
 {
 	switch (level) {

src/native/clr/include/host/gc-bridge.hh

@@ -65,21 +65,9 @@ namespace xamarin::android {
 			return mark_cross_references;
 		}
 
-		static void trigger_java_gc (JNIEnv *env) noexcept;
-
-		// Trigger Java GC using the cached Runtime instance (for managed processing mode)
-		static void trigger_java_gc_cached () noexcept
-		{
-			JNIEnv *env = OSBridge::ensure_jnienv ();
-			trigger_java_gc (env);
-		}
-
 	private:
 		static inline OnMarkCrossReferencesCallback on_mark_cross_references_callback = nullptr;
 
-		static inline jobject Runtime_instance = nullptr;
-		static inline jmethodID Runtime_gc = nullptr;
-
 		static void mark_cross_references (MarkCrossReferencesArgs *args) noexcept;
 
 		static void log_mark_cross_references_args_if_enabled (MarkCrossReferencesArgs *args) noexcept;

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

@@ -18,7 +18,6 @@ extern "C" {
 
 	// Functions for managed GC bridge processing mode
 	BridgeProcessingFtn clr_gc_bridge_initialize_for_managed_processing (OnMarkCrossReferencesCallback callback) noexcept;
-	void clr_gc_bridge_trigger_java_gc () noexcept;
 
 	void monodroid_log (xamarin::android::LogLevel level, LogCategories category, const char *message) noexcept;
 	char* monodroid_TypeManager_get_java_class_name (jclass klass) noexcept;

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

@@ -70,7 +70,6 @@ const std::vector<std::string> internal_pinvoke_names = {
 	"clr_typemap_managed_to_java",
 	"clr_typemap_java_to_managed",
 	"clr_gc_bridge_initialize_for_managed_processing",
-	"clr_gc_bridge_trigger_java_gc",
 	"_monodroid_weak_gref_delete",
 	"_monodroid_weak_gref_get",
 	"_monodroid_weak_gref_new",

src/native/clr/pinvoke-override/pinvoke-tables.include

@@ -11,7 +11,7 @@
 namespace {
 #if INTPTR_MAX == INT64_MAX
 	//64-bit internal p/invoke table
-	std::array<PinvokeEntry, 25> internal_pinvokes {{
+	std::array<PinvokeEntry, 24> internal_pinvokes {{
 		{0x34f89602cc44d0, "clr_gc_bridge_initialize_for_managed_processing", reinterpret_cast<void*>(&clr_gc_bridge_initialize_for_managed_processing)},
 		{0x3b2467e7eadd4a6a, "_monodroid_lref_log_new", reinterpret_cast<void*>(&_monodroid_lref_log_new)},
 		{0x423c8f539a2c56d2, "_monodroid_lookup_replacement_type", reinterpret_cast<void*>(&_monodroid_lookup_replacement_type)},
@@ -29,7 +29,6 @@ namespace {
 		{0xb9bae9c43fb05089, "xamarin_app_init", reinterpret_cast<void*>(&xamarin_app_init)},
 		{0xc2a21d3f6c8ccc24, "_monodroid_lookup_replacement_method_info", reinterpret_cast<void*>(&_monodroid_lookup_replacement_method_info)},
 		{0xc5b4690e13898fa3, "monodroid_timing_start", reinterpret_cast<void*>(&monodroid_timing_start)},
-		{0xcb5109712dd7b398, "clr_gc_bridge_trigger_java_gc", reinterpret_cast<void*>(&clr_gc_bridge_trigger_java_gc)},
 		{0xd1e121b94ea63f2e, "_monodroid_gref_get", reinterpret_cast<void*>(&_monodroid_gref_get)},
 		{0xd5151b00eb33d85e, "monodroid_TypeManager_get_java_class_name", reinterpret_cast<void*>(&monodroid_TypeManager_get_java_class_name)},
 		{0xe27b9849b7e982cb, "_monodroid_max_gref_get", reinterpret_cast<void*>(&_monodroid_max_gref_get)},
@@ -544,10 +543,9 @@ constexpr hash_t system_security_cryptography_native_android_library_hash = 0x18
 constexpr hash_t system_globalization_native_library_hash = 0x28b5c8fca080abd5;
 #else
 	//32-bit internal p/invoke table
-	std::array<PinvokeEntry, 25> internal_pinvokes {{
+	std::array<PinvokeEntry, 24> internal_pinvokes {{
 		{0xb7a486a, "monodroid_TypeManager_get_java_class_name", reinterpret_cast<void*>(&monodroid_TypeManager_get_java_class_name)},
 		{0x1d6638a0, "clr_gc_bridge_initialize_for_managed_processing", reinterpret_cast<void*>(&clr_gc_bridge_initialize_for_managed_processing)},
-		{0x21bee2a0, "clr_gc_bridge_trigger_java_gc", reinterpret_cast<void*>(&clr_gc_bridge_trigger_java_gc)},
 		{0x2aea7c33, "_monodroid_max_gref_get", reinterpret_cast<void*>(&_monodroid_max_gref_get)},
 		{0x3227d81a, "monodroid_timing_start", reinterpret_cast<void*>(&monodroid_timing_start)},
 		{0x333d4835, "_monodroid_lookup_replacement_method_info", reinterpret_cast<void*>(&_monodroid_lookup_replacement_method_info)},
@@ -1077,6 +1075,6 @@ constexpr hash_t system_security_cryptography_native_android_library_hash = 0x93
 constexpr hash_t system_globalization_native_library_hash = 0xa66f1e5a;
 #endif
 
-constexpr size_t internal_pinvokes_count = 25;
+constexpr size_t internal_pinvokes_count = 24;
 constexpr size_t dotnet_pinvokes_count = 491;
 } // end of anonymous namespace

src/native/nativeaot/host/host.cc

@@ -63,7 +63,6 @@ void Host::OnInit (jstring language, jstring filesDir, jstring cacheDir, JnienvI
 
 	OSBridge::initialize_on_runtime_init (env, runtimeClass);
 	GCBridge::initialize_on_runtime_init (env, runtimeClass);
-	// Bridge processing is now done in managed code (C#)
 
 	// We expect the struct to be initialized by the managed land the way it sees fit, we set only the
 	// fields we support.