[CoreCLR] Automatically detach current thread from JNI

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

@@ -17,8 +17,8 @@ void BridgeProcessing::initialize_on_runtime_init (JNIEnv *env, jclass runtimeCl
 	abort_unless (GCUserPeer_class != nullptr && GCUserPeer_ctor != nullptr, "Failed to load mono.android.GCUserPeer!");
 }
 
-BridgeProcessing::BridgeProcessing (MarkCrossReferencesArgs *args) noexcept
-	: env{ OSBridge::ensure_jnienv () },
+BridgeProcessing::BridgeProcessing (JNIEnv *jniEnv, MarkCrossReferencesArgs *args) noexcept
+	: env{ jniEnv },
 	  cross_refs{ args }
 {
 	if (args == nullptr) [[unlikely]] {

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

@@ -53,7 +53,6 @@ void GCBridge::mark_cross_references (MarkCrossReferencesArgs *args) noexcept
 	abort_if_invalid_pointer_argument (args, "args");
 	abort_unless (args->Components != nullptr || args->ComponentCount == 0, "Components must not be null if ComponentCount is greater than 0");
 	abort_unless (args->CrossReferences != nullptr || args->CrossReferenceCount == 0, "CrossReferences must not be null if CrossReferenceCount is greater than 0");
-	log_mark_cross_references_args_if_enabled (args);
 
 	shared_args.store (args);
 	shared_args_semaphore.release ();
@@ -64,31 +63,32 @@ void GCBridge::bridge_processing () noexcept
 	abort_unless (bridge_processing_started_callback != nullptr, "GC bridge processing started callback is not set");
 	abort_unless (bridge_processing_finished_callback != nullptr, "GC bridge processing finished callback is not set");
 
+	JNIEnv *env = OSBridge::ensure_jnienv ();
+
 	while (true) {
 		// wait until mark cross references args are set by the GC callback
 		shared_args_semaphore.acquire ();
 		MarkCrossReferencesArgs *args = shared_args.load ();
+		log_mark_cross_references_args_if_enabled (env, args);
 
 		bridge_processing_started_callback (args);
 
-		BridgeProcessing bridge_processing {args};
+		BridgeProcessing bridge_processing {env, args};
 		bridge_processing.process ();
 
 		bridge_processing_finished_callback (args);
 	}
 }
 
 [[gnu::always_inline]]
-void GCBridge::log_mark_cross_references_args_if_enabled (MarkCrossReferencesArgs *args) noexcept
+void GCBridge::log_mark_cross_references_args_if_enabled (JNIEnv *env, MarkCrossReferencesArgs *args) noexcept
 {
 	if (!Logger::gc_spew_enabled ()) [[likely]] {
 		return;
 	}
 
 	log_info (LOG_GC, "cross references callback invoked with {} sccs and {} xrefs.", args->ComponentCount, args->CrossReferenceCount);
 
-	JNIEnv *env = OSBridge::ensure_jnienv ();
-
 	for (size_t i = 0; i < args->ComponentCount; ++i) {
 		const StronglyConnectedComponent &scc = args->Components [i];
 		log_info (LOG_GC, "group {} with {} objects", i, scc.Count);

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

@@ -23,7 +23,7 @@ struct CrossReferenceTarget
 class BridgeProcessing
 {
 public:
-	BridgeProcessing (MarkCrossReferencesArgs *args) noexcept;
+	BridgeProcessing (JNIEnv *jniEnv, MarkCrossReferencesArgs *args) noexcept;
 	static void initialize_on_runtime_init (JNIEnv *jniEnv, jclass runtimeClass) noexcept;
 	void process () noexcept;
 private:

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

@@ -95,7 +95,7 @@ namespace xamarin::android {
 		static void bridge_processing () noexcept;
 		static void mark_cross_references (MarkCrossReferencesArgs *args) noexcept;
 
-		static void log_mark_cross_references_args_if_enabled (MarkCrossReferencesArgs *args) noexcept;
+		static void log_mark_cross_references_args_if_enabled (JNIEnv *env, MarkCrossReferencesArgs *args) noexcept;
 		static void log_handle_context (JNIEnv *env, HandleContext *ctx) noexcept;
 	};
 }

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

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <cstdio>
+#include <pthread.h>
 
 #include <jni.h>
 
@@ -43,13 +44,30 @@ namespace xamarin::android {
 				args.version = JNI_VERSION_1_6;
 				args.name = nullptr;
 				args.group = nullptr;
-				jvm->AttachCurrentThread (&env, &args);
+				jvm->AttachCurrentThreadAsDaemon (&env, &args);
 				abort_unless (env != nullptr, "Unable to get a valid pointer to JNIEnv");
+
+				(void) pthread_once (&thread_local_env_init_key, make_key);
+				pthread_setspecific (thread_local_env_key, env);
 			}
 
 			return env;
 		}
 
+	private:
+		static inline pthread_key_t thread_local_env_key = {};
+		static inline pthread_once_t thread_local_env_init_key = PTHREAD_ONCE_INIT;
+
+		static void make_key () noexcept
+		{
+			pthread_key_create (&thread_local_env_key, &detach_thread_from_jni);
+		}
+
+		static void detach_thread_from_jni ([[maybe_unused]] void* unused) noexcept
+		{
+			jvm->DetachCurrentThread ();
+		}
+
 	private:
 		static auto _monodroid_gref_inc () noexcept -> int;
 		static auto _monodroid_gref_dec () noexcept -> int;