Lots of code, Android doesn't cooperate...

No matter what I try, the call posted to the main thread still doesn't use
the right class loader and, thus, `System.loadLibrary` cannot find the shared lib:

```
08-13 12:16:10.657 12472 12507 D monodroid-assembly: Trying to load loading shared JNI library /data/user/0/Mono.Android.NET_Tests/files/.__override__/arm64-v8a/libSystem.Security.Cryptography.Native.Android.so with System.loadLibrary
08-13 12:16:10.657 12472 12507 D monodroid-assembly: Running DSO loader on thread 12507, dispatching to main thread
08-13 12:16:10.657 12472 12472 D monodroid-assembly: Looper CB called on thread 12472. Will attempt to load DSO 'System.Security.Cryptography.Native.Android'
08-13 12:16:10.657 12472 12472 D monodroid-assembly: Undecorated library name: System.Security.Cryptography.Native.Android
08-13 12:16:10.659 12472 12472 D nativeloader: Load libSystem.Security.Cryptography.Native.Android.so using system ns (caller=/system/framework/framework.jar!classes3.dex): dlopen failed: library "libSystem.Security.Cryptography.Native.Android.so" not found
08-13 12:16:10.659 12472 12472 D monodroid-assembly: System.loadLibrary threw a Java exception. Will attempt to log it.
08-13 12:16:10.661 12472 12472 W System.err: java.lang.UnsatisfiedLinkError: dlopen failed: library
"libSystem.Security.Cryptography.Native.Android.so" not found
```

Time to think about something else :( Thank you Android for 3 days wasted

Author: grendello

src/native/clr/host/CMakeLists.txt

@@ -28,13 +28,13 @@ set(XAMARIN_NET_ANDROID_STATIC_LIB "${XAMARIN_NET_ANDROID_LIB}-static")
 set(XAMARIN_MONODROID_SOURCES
   assembly-store.cc
   bridge-processing.cc
-  dso-loader.cc
   gc-bridge.cc
   host.cc
   host-jni.cc
   host-util.cc
   internal-pinvokes.cc
   os-bridge.cc
+  runtime-environment.cc
   runtime-util.cc
   typemap.cc
   xamarin_getifaddrs.cc

src/native/clr/host/dso-loader.cc

@@ -0,0 +1,9 @@
+#include <runtime-base/runtime-environment.hh>
+#include <host/os-bridge.hh>
+
+using namespace xamarin::android;
+
+auto RuntimeEnvironment::get_jnienv () noexcept -> JNIEnv*
+{
+	return OSBridge::ensure_jnienv ();
+}

src/native/clr/host/runtime-environment.cc

@@ -11,6 +11,7 @@
 
 #include <runtime-base/android-system.hh>
 #include <runtime-base/mainthread-dso-loader.hh>
+#include <runtime-base/runtime-environment.hh>
 #include <runtime-base/system-loadlibrary-wrapper.hh>
 #include <runtime-base/util.hh>
 #include <shared/helpers.hh>
@@ -27,7 +28,7 @@ namespace xamarin::android {
 		static void init (JNIEnv *env, jclass systemClass, ALooper *main_looper, pid_t _main_thread_id) noexcept
 		{
 			SystemLoadLibraryWrapper::init (env, systemClass);
-			MainThreadDsoLoader::init (main_looper);
+			MainThreadDsoLoader::init (env, main_looper);
 			main_thread_id = _main_thread_id;
 		}
 
@@ -70,7 +71,6 @@ namespace xamarin::android {
 		}
 
 	private:
-		static auto get_jnienv () noexcept -> JNIEnv*;
 		static auto load_jni_on_main_thread (std::string_view const& full_name, std::string const& undecorated_name) noexcept -> void*;
 
 		[[gnu::always_inline]]
@@ -99,10 +99,6 @@ namespace xamarin::android {
 		{
 			log_debug (LOG_ASSEMBLY, "Trying to load loading shared JNI library {} with System.loadLibrary", name);
 
-			if (systemKlass == nullptr) [[unlikely]] {
-				Helpers::abort_application ("DSO loader class not initialized properly."sv);
-			}
-
 			auto get_file_name = [](std::string_view const& full_name, bool is_path) -> std::string_view {
 				if (!is_path) {
 					return full_name;
@@ -163,15 +159,18 @@ namespace xamarin::android {
 
 			// TODO: implement the above
 			if (gettid () == main_thread_id) {
-				if (!SystemLoadLibraryWrapper::load (get_jnienv (), get_undecorated_name (name, name_is_path))) {
+				if (!SystemLoadLibraryWrapper::load (RuntimeEnvironment::get_jnienv (), get_undecorated_name (name, name_is_path))) {
 					// We could abort, but let's let the managed land react to this library missing. We cannot continue
 					// with `dlopen` below, because without `JNI_OnLoad` etc invoked, we might have nasty crashes in the
 					// library code if e.g. it assumes that `JNI_OnLoad` initialized all the Java class, method etc
 					// pointers.
 					return nullptr;
 				}
 			} else {
-				Helpers::abort_application ("Loading DSO on the main thread not implemented yet"sv);
+				MainThreadDsoLoader loader;
+				if (!loader.load (name, get_undecorated_name (name, name_is_path))) {
+					return nullptr;
+				}
 			}
 
 			// This is unfortunate, but since `System.loadLibrary` doesn't return the class handle, we must get it this
@@ -183,8 +182,6 @@ namespace xamarin::android {
 		}
 
 	private:
-		static inline jmethodID System_loadLibrary = nullptr;
-		static inline jclass systemKlass = nullptr;
 		static inline pid_t main_thread_id = 0;
 	};
 }

src/native/common/include/runtime-base/dso-loader.hh

@@ -4,12 +4,17 @@
 #include <cstring>
 #include <unistd.h>
 
+#include <array>
+#include <chrono>
 #include <format>
 #include <semaphore>
 #include <string_view>
 
 #include <android/looper.h>
 
+#include <runtime-base/logger.hh>
+#include <runtime-base/runtime-environment.hh>
+#include <runtime-base/system-loadlibrary-wrapper.hh>
 #include <shared/helpers.hh>
 
 namespace xamarin::android {
@@ -24,7 +29,7 @@ namespace xamarin::android {
 				Helpers::abort_application (
 					LOG_ASSEMBLY,
 					std::format (
-						"Failed to create a pipe for main thread DSO loader. {}",
+						"Failed to create a pipe for main thread DSO loader. {}"sv,
 						strerror (errno)
 					)
 				);
@@ -64,35 +69,89 @@ namespace xamarin::android {
 		MainThreadDsoLoader& operator=(const MainThreadDsoLoader&) = delete;
 		MainThreadDsoLoader& operator=(MainThreadDsoLoader&&) = delete;
 
-		void load (std::string_view const& full_name, std::string const& undecorated_name) noexcept
+		bool load (std::string_view const& full_name, std::string_view const& undecorated_name) noexcept
 		{
-			// TODO: init load here by writing to pipe_fds[1]
+			if (!undecorated_library_name.empty ()) [[unlikely]] {
+				Helpers::abort_application ("Main thread DSO loader object reused! DO NOT DO THAT!"sv);
+			}
+			log_debug (LOG_ASSEMBLY, "Running DSO loader on thread {}, dispatching to main thread"sv, gettid ());
+
+			undecorated_library_name = undecorated_name;
+			load_success = false;
+			constexpr std::array<uint8_t, 1> payload { 0xFF };
+			ssize_t nbytes = write (pipe_fds[1], payload.data (), payload.size ());
+			if (nbytes == -1) {
+				log_warn (
+					LOG_ASSEMBLY,
+					"Write failure when posting a DSO load event to main thread. {}"sv,
+					strerror (errno)
+				);
+				return false;
+			}
 
 			// Wait for the callback to complete
-			load_complete_sem.acquire ();
+			using namespace std::literals;
+
+			// We'll wait for up to 3s, it should be more than enough time for the library to load
+			bool success = load_complete_sem.try_acquire_for (3s);
+			if (!success) {
+				log_warn (LOG_ASSEMBLY, "Timeout while waiting for shared library '{}' to load."sv, full_name);
+				return false;
+			}
+
+			return load_success;
 		}
 
-		static void init (ALooper *main_looper)
+		static void init (JNIEnv *main_jni_env, ALooper *main_looper)
 		{
-			main_thread_looper = main_looper;
+			if (main_thread_looper != nullptr) {
+				return;
+			}
 
+			main_thread_looper = main_looper;
+			main_thread_jni_env = main_jni_env;
 			// This will keep the looper around for the lifetime of the application.
 			ALooper_acquire (main_looper);
 		}
 
 	private:
-		static auto load_cb (int fd, int events, void *data) noexcept -> int
+
+		static auto load_cb ([[maybe_unused]] int fd, [[maybe_unused]] int events, void *data) noexcept -> int
 		{
 			auto self = reinterpret_cast<MainThreadDsoLoader*> (data);
+			if (self == nullptr) [[unlikely]] {
+				Helpers::abort_application ("MainThreadDsoLoader instance not passed to the looper callback."sv);
+			}
+
+			auto over_and_out = [&self]() -> int {
+				// We're one-shot, 0 means just that
+				self->load_complete_sem.release ();
+				return 0;
+			};
+
+			if (self->undecorated_library_name.empty ()) {
+				log_warn (LOG_ASSEMBLY, "Library name not specified in main thread looper callback."sv);
+				return over_and_out ();
+			}
+
+			log_debug (
+				LOG_ASSEMBLY,
+				"Looper CB called on thread {}. Will attempt to load DSO '{}'"sv,
+				gettid (),
+				self->undecorated_library_name
+			);
 
-			self->load_complete_sem.release ();
-			return 0; // We're one-shot, 0 means just that
+			self->load_success = SystemLoadLibraryWrapper::load (main_thread_jni_env /* RuntimeEnvironment::get_jnienv () */, self->undecorated_library_name);
+			return over_and_out ();
 		}
 
 	private:
 		int pipe_fds[2] = {-1, -1};
 		std::binary_semaphore load_complete_sem {0};
+		std::string_view undecorated_library_name {};
+		bool load_success = false;
 
 		static inline ALooper *main_thread_looper = nullptr;
+		static inline JNIEnv *main_thread_jni_env = nullptr;
 	};
 }

src/native/common/include/runtime-base/mainthread-dso-loader.hh

@@ -0,0 +1,11 @@
+#pragma once
+
+#include <jni.h>
+
+namespace xamarin::android {
+	class RuntimeEnvironment
+	{
+	public:
+		static auto get_jnienv () noexcept -> JNIEnv*;
+	};
+}

src/native/common/include/runtime-base/runtime-environment.hh

@@ -25,6 +25,10 @@ namespace xamarin::android {
 		[[gnu::flatten]]
 		static auto load (JNIEnv *jni_env, std::string_view const& undecorated_lib_name) noexcept -> bool
 		{
+			if (systemKlass == nullptr) [[unlikely]] {
+				Helpers::abort_application ("System.loadeLibrary wrapper class not initialized properly."sv);
+			}
+
 			// std::string is needed because we must pass a NUL-terminated string to Java, otherwise
 			// strange things happen (and std::string_view is not necessarily such a string)
 			const std::string lib_name { undecorated_lib_name };

src/native/common/include/runtime-base/system-loadlibrary-wrapper.hh

@@ -93,7 +93,6 @@ set(XAMARIN_MONO_ANDROID_STATIC_LIB "${XAMARIN_MONO_ANDROID_LIB}-static")
 set(XAMARIN_MONODROID_SOURCES
   debug-constants.cc
   debug.cc
-  dso-loader.cc
   embedded-assemblies-zip.cc
   embedded-assemblies.cc
   globals.cc
@@ -104,6 +103,7 @@ set(XAMARIN_MONODROID_SOURCES
   monodroid-tracing.cc
   monovm-properties.cc
   osbridge.cc
+  runtime-environment.cc
   runtime-util.cc
   timezones.cc
   xamarin_getifaddrs.cc

src/native/mono/monodroid/CMakeLists.txt

@@ -1,11 +1,11 @@
-#include <runtime-base/dso-loader.hh>
+#include <runtime-base/runtime-environment.hh>
 
 #include "osbridge.hh"
 
 using namespace xamarin::android;
 using namespace xamarin::android::internal;
 
-auto DsoLoader::get_jnienv () noexcept -> JNIEnv*
+auto RuntimeEnvironment::get_jnienv () noexcept -> JNIEnv*
 {
 	return OSBridge::ensure_jnienv ();
 }

src/native/mono/monodroid/dso-loader.cc renamed to src/native/mono/monodroid/runtime-environment.cc

@@ -2,7 +2,7 @@ set(LIB_NAME xamarin-debug-app-helper)
 set(LIB_ALIAS xa::debug-app-helper)
 
 set(XAMARIN_DEBUG_HELPER_SOURCES
-  ../monodroid/dso-loader.cc
+  ../monodroid/runtime-environment.cc
   debug-app-helper.cc
 )
 add_clang_check_sources("${XAMARIN_DEBUG_HELPER_SOURCES}")
@@ -55,6 +55,7 @@ target_link_libraries(
   xa::runtime-base
   xa::java-interop
   -ldl
+  -landroid
   -llog
   -lmonosgen-2.0
 )