Optimize startup a tiny bit

Use `std::span` and `std::array` for application library directories in
a way that allows us to avoid memory allocation in the most common
scenario (where shared libraries aren't extraced to the filesystem but
reside in one of the split apks)

src/monodroid/jni/android-system.cc

@@ -403,7 +403,7 @@ AndroidSystem::load_dso_from_specified_dirs (const char **directories, size_t nu
 void*
 AndroidSystem::load_dso_from_app_lib_dirs (const char *name, unsigned int dl_flags)
 {
-	return load_dso_from_specified_dirs (static_cast<const char**> (app_lib_directories), app_lib_directories_size, name, dl_flags);
+	return load_dso_from_specified_dirs (app_lib_directories.data (), app_lib_directories.size (), name, dl_flags);
 }
 
 void*
@@ -448,9 +448,10 @@ AndroidSystem::get_full_dso_path_on_disk (const char *dso_name, dynamic_local_st
 			return true;
 	}
 #endif
-	for (size_t i = 0; i < app_lib_directories_size; i++) {
-		if (get_existing_dso_path_on_disk (app_lib_directories [i], dso_name, path))
+	for (const char *app_lib_dir : app_lib_directories) {
+		if (get_existing_dso_path_on_disk (app_lib_dir, dso_name, path)) {
 			return true;
+		}
 	}
 
 	return false;

src/monodroid/jni/basic-android-system.cc

@@ -1,16 +1,10 @@
-#include <cerrno>
-
 #include "basic-android-system.hh"
 #include "cpp-util.hh"
 #include "globals.hh"
 
 using namespace xamarin::android;
 using namespace xamarin::android::internal;
 
-const char **BasicAndroidSystem::app_lib_directories;
-size_t BasicAndroidSystem::app_lib_directories_size = 0;
-const char* BasicAndroidSystem::built_for_abi_name = nullptr;
-
 void
 BasicAndroidSystem::detect_embedded_dso_mode (jstring_array_wrapper& appDirs) noexcept
 {
@@ -31,14 +25,21 @@ BasicAndroidSystem::setup_app_library_directories (jstring_array_wrapper& runtim
 {
 	if (!is_embedded_dso_mode_enabled ()) {
 		log_debug (LOG_DEFAULT, "Setting up for DSO lookup in app data directories");
-		BasicAndroidSystem::app_lib_directories_size = 1;
-		BasicAndroidSystem::app_lib_directories = new const char*[app_lib_directories_size]();
+
+		BasicAndroidSystem::app_lib_directories = std::span<const char*> (single_app_lib_directory);
 		BasicAndroidSystem::app_lib_directories [0] = utils.strdup_new (appDirs[SharedConstants::APP_DIRS_DATA_DIR_INDEX].get_cstr ());
 		log_debug (LOG_ASSEMBLY, "Added filesystem DSO lookup location: %s", appDirs[SharedConstants::APP_DIRS_DATA_DIR_INDEX].get_cstr ());
 	} else {
 		log_debug (LOG_DEFAULT, "Setting up for DSO lookup directly in the APK");
-		BasicAndroidSystem::app_lib_directories_size = runtimeApks.get_length ();
-		BasicAndroidSystem::app_lib_directories = new const char*[app_lib_directories_size]();
+
+		if (have_split_apks) {
+			// If split apks are used, then we will have just a single app library directory. Don't allocate any memory
+			// dynamically in this case
+			BasicAndroidSystem::app_lib_directories = std::span<const char*> (single_app_lib_directory);
+		} else {
+			size_t app_lib_directories_size = have_split_apks ? 1 : runtimeApks.get_length ();
+			BasicAndroidSystem::app_lib_directories = std::span<const char*> (new const char*[app_lib_directories_size], app_lib_directories_size);
+		}
 
 		unsigned short built_for_cpu = 0, running_on_cpu = 0;
 		unsigned char is64bit = 0;
@@ -61,7 +62,7 @@ BasicAndroidSystem::for_each_apk (jstring_array_wrapper &runtimeApks, ForEachApk
 force_inline void
 BasicAndroidSystem::add_apk_libdir (const char *apk, size_t &index, const char *abi) noexcept
 {
-	abort_unless (index < app_lib_directories_size, "Index out of range");
+	abort_unless (index < app_lib_directories.size (), "Index out of range");
 	app_lib_directories [index] = utils.string_concat (apk, "!/lib/", abi);
 	log_debug (LOG_ASSEMBLY, "Added APK DSO lookup location: %s", app_lib_directories[index]);
 	index++;
@@ -87,7 +88,12 @@ BasicAndroidSystem::setup_apk_directories (unsigned short running_on_cpu, jstrin
 		}
 	}
 
-	app_lib_directories_size = number_of_added_directories;
+	if (app_lib_directories.size () == number_of_added_directories) [[likely]] {
+		return;
+	}
+
+	abort_unless (number_of_added_directories > 0, "At least a single application lib directory must be added");
+	app_lib_directories = app_lib_directories.subspan (0, number_of_added_directories);
 }
 
 char*

src/monodroid/jni/basic-android-system.hh

@@ -4,6 +4,7 @@
 #include <array>
 #include <cstddef>
 #include <cstdint>
+#include <span>
 
 #include "cpu-arch.hh"
 #include "jni-wrappers.hh"
@@ -33,7 +34,7 @@ namespace xamarin::android::internal
 #pragma clang diagnostic pop
 #endif
 		static constexpr size_t ANDROID_ABI_NAMES_SIZE = sizeof(android_abi_names) / sizeof (android_abi_names[0]);
-		static const char* built_for_abi_name;
+		inline static const char* built_for_abi_name = nullptr;
 
 	public:
 #ifdef ANDROID64
@@ -52,9 +53,12 @@ namespace xamarin::android::internal
 		static constexpr char SYSTEM_LIB_PATH[] = "";
 #endif
 
-		inline static std::array<char*, 1> override_dirs;
-		static const char **app_lib_directories;
-		static size_t app_lib_directories_size;
+		inline static std::array<char*, 1> override_dirs{};
+
+		// This optimizes things a little bit. The array is allocated at build time, so we pay no cost for its
+		// allocation and at run time it allows us to skip dynamic memory allocation.
+		inline static std::array<const char*, 1> single_app_lib_directory{};
+		inline static std::span<const char*> app_lib_directories;
 		static const char* get_built_for_abi_name ();
 
 	public:

src/monodroid/jni/debug-app-helper.cc

@@ -216,8 +216,8 @@ get_libmonosgen_path ()
 		}
 	}
 
-	for (size_t i = 0; i < BasicAndroidSystem::app_lib_directories_size; i++) {
-		if (runtime_exists (BasicAndroidSystem::app_lib_directories [i], libmonoso)) {
+	for (const char *app_lib_dir : BasicAndroidSystem::app_lib_directories) {
+		if (runtime_exists (app_lib_dir, libmonoso)) {
 			return libmonoso;
 		}
 	}
@@ -270,8 +270,8 @@ get_libmonosgen_path ()
 		log_fatal (LOG_DEFAULT, "  %s", od);
 	}
 
-	for (size_t i = 0; i < BasicAndroidSystem::app_lib_directories_size; i++) {
-		log_fatal (LOG_DEFAULT, "  %s", BasicAndroidSystem::app_lib_directories [i]);
+	for (const char *app_lib_dir : BasicAndroidSystem::app_lib_directories) {
+		log_fatal (LOG_DEFAULT, "  %s", app_lib_dir);
 	}
 
 	log_fatal (LOG_DEFAULT, "Do you have a shared runtime build of your app with AndroidManifest.xml android:minSdkVersion < 10 while running on a 64-bit Android 5.0 target? This combination is not supported.");