[native, Mono.Android] GC bridge logging improvements

Context: #9039

While trying to further diagnose #9039, @jonpryor started fearing
that a GC bridge issue might be at play, but the current GC bridge
logging could use some improvements.

Update `OSBridge::take_weak_global_ref_jni()` to do two things:

 1. Set the `handle` and `handle_type` fields *before* deleting the
    original GREF.  This is for a hypothetical thread-safety issue
    wherein the `handle` field and the `Handle` property could return
    a *deleted* GREF before being updated to the "new" Weak GREF.

    We have not seen this as being an issue in practice, but it's
    something we noticed.

 2. Update the `from` parameter text to `_monodroid_weak_gref_new()`
    to look more like a stack trace.

    Previously, the GREF log would contain entries such as:

        monodroid-gref: -g- grefc 441 gwrefc 1 handle 0x4fda/G from thread 'finalizer'(17269)
        monodroid-gref: take_weak_global_ref_jni

    making me wonder "why is `take_weak_global_ref_jni` there?!"

    It's there because of the "from" parameter, to provide context.
    Update it to instead read:

        monodroid-gref: -g- grefc 441 gwrefc 1 handle 0x4fda/G from thread 'finalizer'(17269)
        monodroid-gref:    at [[gc:take_weak_global_ref_jni]]

    which makes it clearer what's intended.

Update `OSBridge::take_global_ref_jni()` in a similar manner.

Update other `_monodroid*_gref_*()` call sites to update *their*
`from` parameters accordingly.

Update `AndroidRuntime.FinalizePeer()` so that the messages it logs
are actually useful.  Currently they are:

	Finalizing handle 0x0/G

which leaves a lot to be desired.  Update it to instead read:

	Finalizing Instance.Type=Example.Whatever PeerReference=0x0/G IdentityHashCode=0x123456 Instance=0xdeadbeef

"Promote" `LOG_GC` to work in Release builds as well.  This means
that both:

	adb shell setprop debug.mono.log gc
	adb shell setprop debug.mono.gc 1

will work with `libmono-android.release.so`, i.e. Release builds
of apps.

Update `OSBridge::gc_cross_references()` log the `handle` field of
bridged instances.

src/Mono.Android/Android.Runtime/AndroidRuntime.cs

@@ -846,7 +846,13 @@ public override void FinalizePeer (IJavaPeerable value)
 				throw new ArgumentNullException (nameof (value));
 
 			if (Logger.LogGlobalRef) {
-				RuntimeNativeMethods._monodroid_gref_log ($"Finalizing handle {value.PeerReference}\n");
+				RuntimeNativeMethods._monodroid_gref_log (
+						string.Format (CultureInfo.InvariantCulture,
+							"Finalizing Instance.Type={0} PeerReference={1} IdentityHashCode=0x{2:x} Instance=0x{3:x}",
+							value.GetType ().ToString (),
+							value.PeerReference.ToString (),
+							value.JniIdentityHashCode,
+							RuntimeHelpers.GetHashCode (value)));
 			}
 
 			// FIXME: need hash cleanup mechanism.

src/native/monodroid/monodroid-glue.cc

@@ -965,7 +965,6 @@ MonodroidRuntime::propagate_uncaught_exception (JNIEnv *env, jobject javaThread,
 	mono_runtime_invoke (method, nullptr, args, nullptr);
 }
 
-#if DEBUG
 static void
 setup_gc_logging (void)
 {
@@ -974,7 +973,6 @@ setup_gc_logging (void)
 		log_categories |= LOG_GC;
 	}
 }
-#endif
 
 inline void
 MonodroidRuntime::set_environment_variable_for_directory (const char *name, jstring_wrapper &value, bool createDirectory, mode_t mode)
@@ -1431,8 +1429,9 @@ MonodroidRuntime::Java_mono_android_Runtime_initInternal (JNIEnv *env, jclass kl
 
 	Logger::init_reference_logging (AndroidSystem::get_primary_override_dir ());
 
-#if DEBUG
 	setup_gc_logging ();
+
+#if DEBUG
 	set_debug_env_vars ();
 #endif
 

src/native/monodroid/osbridge.cc

@@ -461,18 +461,16 @@ OSBridge::take_global_ref_jni (JNIEnv *env, MonoObject *obj)
 		_monodroid_gref_log_new (weak, get_object_ref_type (env, weak),
 				handle, get_object_ref_type (env, handle),
 				"finalizer", gettid (),
-				"take_global_ref_jni", 0);
+				"   at [[gc:take_global_ref_jni]]", 0);
 	}
-	_monodroid_weak_gref_delete (weak, get_object_ref_type (env, weak),
-			"finalizer", gettid (), "take_global_ref_jni", 0);
-	env->DeleteWeakGlobalRef (weak);
-	if (!handle) {
-		void *old_handle = nullptr;
 
-		mono_field_get_value (obj, bridge_info->handle, &old_handle);
-	}
 	mono_field_set_value (obj, bridge_info->handle, &handle);
 	mono_field_set_value (obj, bridge_info->handle_type, &type);
+
+	_monodroid_weak_gref_delete (weak, get_object_ref_type (env, weak),
+			"finalizer", gettid (), "   at [[gc:take_global_ref_jni]]", 0);
+	env->DeleteWeakGlobalRef (weak);
+
 	return handle != nullptr;
 }
 
@@ -495,13 +493,14 @@ OSBridge::take_weak_global_ref_jni (JNIEnv *env, MonoObject *obj)
 	weak = env->NewWeakGlobalRef (handle);
 	_monodroid_weak_gref_new (handle, get_object_ref_type (env, handle),
 			weak, get_object_ref_type (env, weak),
-			"finalizer", gettid (), "take_weak_global_ref_jni", 0);
+			"finalizer", gettid (), "   at [[gc:take_weak_global_ref_jni]]", 0);
 
-	_monodroid_gref_log_delete (handle, get_object_ref_type (env, handle),
-			"finalizer", gettid (), "take_weak_global_ref_jni", 0);
-	env->DeleteGlobalRef (handle);
 	mono_field_set_value (obj, bridge_info->handle, &weak);
 	mono_field_set_value (obj, bridge_info->handle_type, &type);
+
+	_monodroid_gref_log_delete (handle, get_object_ref_type (env, handle),
+			"finalizer", gettid (), "   at [[gc:take_weak_global_ref_jni]]", 0);
+	env->DeleteGlobalRef (handle);
 	return 1;
 }
 
@@ -903,7 +902,6 @@ OSBridge::gc_cross_references (int num_sccs, MonoGCBridgeSCC **sccs, int num_xre
 	if (gc_disabled)
 		return;
 
-#if DEBUG
 	if (Logger::gc_spew_enabled ()) {
 		int i, j;
 		log_info (LOG_GC, "cross references callback invoked with %d sccs and %d xrefs.", num_sccs, num_xrefs);
@@ -912,11 +910,18 @@ OSBridge::gc_cross_references (int num_sccs, MonoGCBridgeSCC **sccs, int num_xre
 			log_info (LOG_GC, "group %d with %d objects", i, sccs [i]->num_objs);
 			for (j = 0; j < sccs [i]->num_objs; ++j) {
 				MonoObject *obj = sccs [i]->objs [j];
+
+				MonoJavaGCBridgeInfo    *bridge_info    = get_gc_bridge_info_for_object (obj);
+				jobject handle = 0;
+				if (bridge_info != nullptr) {
+					mono_field_get_value (obj, bridge_info->handle, &handle);
+				}
 				MonoClass *klass = mono_object_get_class (obj);
-				log_info (LOG_GC, "\tobj %p [%s::%s]",
+				log_info (LOG_GC, "\tobj %p [%s::%s] handle %p",
 						obj,
 						mono_class_get_namespace (klass),
-						mono_class_get_name (klass));
+						mono_class_get_name (klass),
+						handle);
 			}
 		}
 
@@ -925,7 +930,6 @@ OSBridge::gc_cross_references (int num_sccs, MonoGCBridgeSCC **sccs, int num_xre
 				log_info_nocheck (LOG_GC, "xref [%d] %d -> %d", i, xrefs [i].src_scc_index, xrefs [i].dst_scc_index);
 		}
 	}
-#endif
 
 	env = ensure_jnienv ();
 

src/native/runtime-base/logger.cc

@@ -239,8 +239,6 @@ Logger::init_logging_categories (char*& mono_log_mask, char*& mono_log_level) no
 #endif
 	}
 
-#if DEBUG
 	if ((log_categories & LOG_GC) != 0)
 		_gc_spew_enabled = 1;
-#endif  /* DEBUG */
 }

src/native/runtime-base/logger.hh

@@ -30,6 +30,7 @@ namespace xamarin::android {
 		{
 			return _debugger_log_level;
 		}
+#endif // def DEBUG
 
 		static void set_gc_spew_enabled (int yesno) noexcept
 		{
@@ -40,7 +41,6 @@ namespace xamarin::android {
 		{
 			return _gc_spew_enabled;
 		}
-#endif // def DEBUG
 
 	private:
 		static bool set_category (std::string_view const& name, internal::string_segment& arg, unsigned int entry, bool arg_starts_with_name = false) noexcept;
@@ -50,8 +50,8 @@ namespace xamarin::android {
 #if defined(DEBUG)
 		static inline bool _got_debugger_log_level = false;
 		static inline int _debugger_log_level = 0;
-		static inline int _gc_spew_enabled = 0;
 #endif // def DEBUG
+		static inline int _gc_spew_enabled = 0;
 	};
 }
 #endif