[threads] Add a global "runtime startup is finished" flag (dotnet#32668)

This contributes to mono/mono#18916 (to make coop locking not bother with state transitions if the runtime isn't ready yet) .

Co-authored-by: Aleksey Kliger (λgeek) <[email protected]>

src/mono/mono/mini/mini-runtime.c

@@ -4389,6 +4389,7 @@ mini_init (const char *filename, const char *runtime_version)
 	mono_thread_attach (domain);
 	MONO_PROFILER_RAISE (thread_name, (MONO_NATIVE_THREAD_ID_TO_UINT (mono_native_thread_id_get ()), "Main"));
 #endif
+	mono_threads_set_runtime_startup_finished ();
 
 #ifdef ENABLE_EXPERIMENT_TIERED
 	if (!mono_compile_aot) {

src/mono/mono/utils/mono-threads-coop.c

@@ -794,3 +794,11 @@ mono_thread_get_coop_aware (void)
 
 	return result;
 }
+
+char mono_threads_is_runtime_startup_finished_hidden_do_not_modify;
+
+void
+mono_threads_set_runtime_startup_finished (void)
+{
+	mono_threads_is_runtime_startup_finished_hidden_do_not_modify = 1;
+}

src/mono/mono/utils/mono-threads-coop.h

@@ -151,4 +151,15 @@ G_EXTERN_C // due to THREAD_INFO_TYPE varying
 gpointer
 mono_threads_enter_gc_unsafe_region_unbalanced_with_info (THREAD_INFO_TYPE *info, MonoStackData *stackdata);
 
+extern char mono_threads_is_runtime_startup_finished_hidden_do_not_modify;
+
+static inline gboolean
+mono_threads_is_runtime_startup_finished (void)
+{
+	return mono_threads_is_runtime_startup_finished_hidden_do_not_modify != 0;
+}
+
+void
+mono_threads_set_runtime_startup_finished (void);
+
 #endif