Support multithreading for NativeScriptLanguage

Godot may call property setters from non-main thread when an object is
loaded in the edtior. This means NativeScriptLanguage could be accessed
from different threads, but it was not designed for thread-safety.
Besides, previous behaviour made it so that godot_nativescript_init and
godot_gdnative_init could be invoked from non-main thread, while
godot_gdnative_thread is always invoked on the main thread. This may
not be expected by the binding library.

This commit defers native library initialization to the main thread and
adds godot_nativescript_thread_enter and godot_nativescript_thread_exit
callbacks to make a binding library aware of foreign threads.

1 files changed, 28 insertions, 0 deletions

diff --git a/modules/nativescript/nativescript.h b/modules/nativescript/nativescript.h
index bc7a6e3ed6..cf3a64e9b8 100644
--- a/modules/nativescript/nativescript.h
+++ b/modules/nativescript/nativescript.h
@@ -41,6 +41,10 @@
 #include "godot_nativescript.h"
 #include "modules/gdnative/gdnative.h"
 
+#ifndef NO_THREADS
+#include "os/mutex.h"
+#endif
+
 struct NativeScriptDesc {
 
 	struct Method {
@@ -197,6 +201,19 @@ private:
 
 	void _unload_stuff();
 
+#ifndef NO_THREADS
+	Mutex *mutex;
+
+	Set<Ref<GDNativeLibrary> > libs_to_init;
+	Set<NativeScript *> scripts_to_register;
+	volatile bool has_objects_to_register; // so that we don't lock mutex every frame - it's rarely needed
+	void defer_init_library(Ref<GDNativeLibrary> lib, NativeScript *script);
+#endif
+
+	void init_library(const Ref<GDNativeLibrary> &lib);
+	void register_script(NativeScript *script);
+	void unregister_script(NativeScript *script);
+
 public:
 	Map<String, Map<StringName, NativeScriptDesc> > library_classes;
 	Map<String, Ref<GDNative> > library_gdnatives;
@@ -206,6 +223,10 @@ public:
 	const StringName _init_call_type = "nativescript_init";
 	const StringName _init_call_name = "godot_nativescript_init";
 
+	const StringName _thread_cb_call_type = "godot_nativescript_thread_cb";
+	const StringName _thread_enter_call_name = "godot_nativescript_thread_enter";
+	const StringName _thread_exit_call_name = "godot_nativescript_thread_exit";
+
 	NativeScriptLanguage();
 	~NativeScriptLanguage();
 
@@ -215,6 +236,13 @@ public:
 
 	void _hacky_api_anchor();
 
+#ifndef NO_THREADS
+	virtual void thread_enter();
+	virtual void thread_exit();
+
+	virtual void frame();
+#endif
+
 	virtual String get_name() const;
 	virtual void init();
 	virtual String get_type() const;