Merge pull request #36640 from reduz/resource-loader-refactor

Removed ResourceInteractiveLoader, add built-in threaded loading.

1 files changed, 372 insertions, 224 deletions

diff --git a/core/io/resource_loader.cpp b/core/io/resource_loader.cpp
index b43cd7f1a2..504dbe2d63 100644
--- a/core/io/resource_loader.cpp
+++ b/core/io/resource_loader.cpp
@@ -39,26 +39,16 @@
 #include "core/translation.h"
 #include "core/variant_parser.h"
 
+#ifdef DEBUG_LOAD_THREADED
+#define print_lt(m_text) print_line(m_text)
+#else
+#define print_lt(m_text)
+#endif
+
 Ref<ResourceFormatLoader> ResourceLoader::loader[ResourceLoader::MAX_LOADERS];
 
 int ResourceLoader::loader_count = 0;
 
-Error ResourceInteractiveLoader::wait() {
-
-	Error err = poll();
-	while (err == OK) {
-		err = poll();
-	}
-
-	return err;
-}
-
-ResourceInteractiveLoader::~ResourceInteractiveLoader() {
-	if (path_loading != String()) {
-		ResourceLoader::_remove_from_loading_map_and_thread(path_loading, path_loading_thread);
-	}
-}
-
 bool ResourceFormatLoader::recognize_path(const String &p_path, const String &p_for_type) const {
 
 	String extension = p_path.get_extension();
@@ -111,45 +101,6 @@ void ResourceLoader::get_recognized_extensions_for_type(const String &p_type, Li
 	}
 }
 
-void ResourceInteractiveLoader::_bind_methods() {
-
-	ClassDB::bind_method(D_METHOD("get_resource"), &ResourceInteractiveLoader::get_resource);
-	ClassDB::bind_method(D_METHOD("poll"), &ResourceInteractiveLoader::poll);
-	ClassDB::bind_method(D_METHOD("wait"), &ResourceInteractiveLoader::wait);
-	ClassDB::bind_method(D_METHOD("get_stage"), &ResourceInteractiveLoader::get_stage);
-	ClassDB::bind_method(D_METHOD("get_stage_count"), &ResourceInteractiveLoader::get_stage_count);
-}
-
-class ResourceInteractiveLoaderDefault : public ResourceInteractiveLoader {
-
-	GDCLASS(ResourceInteractiveLoaderDefault, ResourceInteractiveLoader);
-
-public:
-	Ref<Resource> resource;
-
-	virtual void set_local_path(const String &p_local_path) { /*scene->set_filename(p_local_path);*/
-	}
-	virtual Ref<Resource> get_resource() { return resource; }
-	virtual Error poll() { return ERR_FILE_EOF; }
-	virtual int get_stage() const { return 1; }
-	virtual int get_stage_count() const { return 1; }
-	virtual void set_translation_remapped(bool p_remapped) { resource->set_as_translation_remapped(p_remapped); }
-
-	ResourceInteractiveLoaderDefault() {}
-};
-
-Ref<ResourceInteractiveLoader> ResourceFormatLoader::load_interactive(const String &p_path, const String &p_original_path, Error *r_error) {
-
-	//either this
-	Ref<Resource> res = load(p_path, p_original_path, r_error);
-	if (res.is_null())
-		return Ref<ResourceInteractiveLoader>();
-
-	Ref<ResourceInteractiveLoaderDefault> ril = Ref<ResourceInteractiveLoaderDefault>(memnew(ResourceInteractiveLoaderDefault));
-	ril->resource = res;
-	return ril;
-}
-
 bool ResourceFormatLoader::exists(const String &p_path) const {
 	return FileAccess::exists(p_path); //by default just check file
 }
@@ -168,10 +119,10 @@ void ResourceFormatLoader::get_recognized_extensions(List<String> *p_extensions)
 	}
 }
 
-RES ResourceFormatLoader::load(const String &p_path, const String &p_original_path, Error *r_error) {
+RES ResourceFormatLoader::load(const String &p_path, const String &p_original_path, Error *r_error, bool p_use_sub_threads, float *r_progress) {
 
 	if (get_script_instance() && get_script_instance()->has_method("load")) {
-		Variant res = get_script_instance()->call("load", p_path, p_original_path);
+		Variant res = get_script_instance()->call("load", p_path, p_original_path, p_use_sub_threads);
 
 		if (res.get_type() == Variant::INT) {
 
@@ -184,29 +135,11 @@ RES ResourceFormatLoader::load(const String &p_path, const String &p_original_pa
 				*r_error = OK;
 			return res;
 		}
-	}
-
-	//or this must be implemented
-	Ref<ResourceInteractiveLoader> ril = load_interactive(p_path, p_original_path, r_error);
-	if (!ril.is_valid())
-		return RES();
-	ril->set_local_path(p_original_path);
-
-	while (true) {
-
-		Error err = ril->poll();
-
-		if (err == ERR_FILE_EOF) {
-			if (r_error)
-				*r_error = OK;
-			return ril->get_resource();
-		}
 
-		if (r_error)
-			*r_error = err;
-
-		ERR_FAIL_COND_V_MSG(err != OK, RES(), "Failed to load resource '" + p_path + "'.");
+		return res;
 	}
+
+	ERR_FAIL_V_MSG(RES(), "Failed to load resource '" + p_path + "', ResourceFormatLoader::load was not implemented for this resource type.");
 }
 
 void ResourceFormatLoader::get_dependencies(const String &p_path, List<String> *p_dependencies, bool p_add_types) {
@@ -256,7 +189,7 @@ void ResourceFormatLoader::_bind_methods() {
 
 ///////////////////////////////////
 
-RES ResourceLoader::_load(const String &p_path, const String &p_original_path, const String &p_type_hint, bool p_no_cache, Error *r_error) {
+RES ResourceLoader::_load(const String &p_path, const String &p_original_path, const String &p_type_hint, bool p_no_cache, Error *r_error, bool p_use_sub_threads, float *r_progress) {
 
 	bool found = false;
 
@@ -267,7 +200,7 @@ RES ResourceLoader::_load(const String &p_path, const String &p_original_path, c
 			continue;
 		}
 		found = true;
-		RES res = loader[i]->load(p_path, p_original_path != String() ? p_original_path : p_path, r_error);
+		RES res = loader[i]->load(p_path, p_original_path != String() ? p_original_path : p_path, r_error, p_use_sub_threads, r_progress);
 		if (res.is_null()) {
 			continue;
 		}
@@ -285,49 +218,68 @@ RES ResourceLoader::_load(const String &p_path, const String &p_original_path, c
 	ERR_FAIL_V_MSG(RES(), "No loader found for resource: " + p_path + ".");
 }
 
-bool ResourceLoader::_add_to_loading_map(const String &p_path) {
+void ResourceLoader::_thread_load_function(void *p_userdata) {
 
-	bool success;
-	MutexLock lock(loading_map_mutex);
+	ThreadLoadTask &load_task = *(ThreadLoadTask *)p_userdata;
+	load_task.loader_id = Thread::get_caller_id();
 
-	LoadingMapKey key;
-	key.path = p_path;
-	key.thread = Thread::get_caller_id();
+	if (load_task.semaphore) {
+		//this is an actual thread, so wait for Ok fom semaphore
+		thread_load_semaphore->wait(); //wait until its ok to start loading
+	}
+	load_task.resource = _load(load_task.remapped_path, load_task.remapped_path != load_task.local_path ? load_task.local_path : String(), load_task.type_hint, false, &load_task.error, load_task.use_sub_threads, &load_task.progress);
+
+	load_task.progress = 1.0; //it was fully loaded at this point, so force progress to 1.0
 
-	if (loading_map.has(key)) {
-		success = false;
+	thread_load_mutex->lock();
+	if (load_task.error != OK) {
+		load_task.status = THREAD_LOAD_FAILED;
 	} else {
-		loading_map[key] = true;
-		success = true;
+		load_task.status = THREAD_LOAD_LOADED;
 	}
+	if (load_task.semaphore) {
 
-	return success;
-}
+		if (load_task.start_next && thread_waiting_count > 0) {
+			thread_waiting_count--;
+			//thread loading count remains constant, this ends but another one begins
+			thread_load_semaphore->post();
+		} else {
+			thread_loading_count--; //no threads waiting, just reduce loading count
+		}
 
-void ResourceLoader::_remove_from_loading_map(const String &p_path) {
-	MutexLock lock(loading_map_mutex);
+		print_lt("END: load count: " + itos(thread_loading_count) + " / wait count: " + itos(thread_waiting_count) + " / suspended count: " + itos(thread_suspended_count) + " / active: " + itos(thread_loading_count - thread_suspended_count));
 
-	LoadingMapKey key;
-	key.path = p_path;
-	key.thread = Thread::get_caller_id();
+		for (int i = 0; i < load_task.poll_requests; i++) {
+			load_task.semaphore->post();
+		}
+		memdelete(load_task.semaphore);
+		load_task.semaphore = nullptr;
+	}
 
-	loading_map.erase(key);
-}
+	if (load_task.resource.is_valid()) {
+		load_task.resource->set_path(load_task.local_path);
 
-void ResourceLoader::_remove_from_loading_map_and_thread(const String &p_path, Thread::ID p_thread) {
-	MutexLock lock(loading_map_mutex);
+		if (load_task.xl_remapped)
+			load_task.resource->set_as_translation_remapped(true);
 
-	LoadingMapKey key;
-	key.path = p_path;
-	key.thread = p_thread;
+#ifdef TOOLS_ENABLED
 
-	loading_map.erase(key);
-}
+		load_task.resource->set_edited(false);
+		if (timestamp_on_load) {
+			uint64_t mt = FileAccess::get_modified_time(load_task.remapped_path);
+			//printf("mt %s: %lli\n",remapped_path.utf8().get_data(),mt);
+			load_task.resource->set_last_modified_time(mt);
+		}
+#endif
 
-RES ResourceLoader::load(const String &p_path, const String &p_type_hint, bool p_no_cache, Error *r_error) {
+		if (_loaded_callback) {
+			_loaded_callback(load_task.resource, load_task.local_path);
+		}
+	}
 
-	if (r_error)
-		*r_error = ERR_CANT_OPEN;
+	thread_load_mutex->unlock();
+}
+Error ResourceLoader::load_threaded_request(const String &p_path, const String &p_type_hint, bool p_use_sub_threads, const String &p_source_resource) {
 
 	String local_path;
 	if (p_path.is_rel_path())
@@ -335,88 +287,154 @@ RES ResourceLoader::load(const String &p_path, const String &p_type_hint, bool p
 	else
 		local_path = ProjectSettings::get_singleton()->localize_path(p_path);
 
-	if (!p_no_cache) {
+	thread_load_mutex->lock();
 
-		{
-			bool success = _add_to_loading_map(local_path);
-			ERR_FAIL_COND_V_MSG(!success, RES(), "Resource: '" + local_path + "' is already being loaded. Cyclic reference?");
+	if (p_source_resource != String()) {
+		//must be loading from this resource
+		if (!thread_load_tasks.has(p_source_resource)) {
+			thread_load_mutex->unlock();
+			ERR_FAIL_V_MSG(ERR_INVALID_PARAMETER, "There is no thread loading source resource '" + p_source_resource + "'.");
+		}
+		//must be loading from this thread
+		if (thread_load_tasks[p_source_resource].loader_id != Thread::get_caller_id()) {
+			thread_load_mutex->unlock();
+			ERR_FAIL_V_MSG(ERR_INVALID_PARAMETER, "Threading loading resource'" + local_path + " failed: Source specified: '" + p_source_resource + "' but was not called by it.");
 		}
 
-		//lock first if possible
-		if (ResourceCache::lock) {
-			ResourceCache::lock->read_lock();
+		//must not be already added as s sub tasks
+		if (thread_load_tasks[p_source_resource].sub_tasks.has(local_path)) {
+			thread_load_mutex->unlock();
+			ERR_FAIL_V_MSG(ERR_INVALID_PARAMETER, "Thread loading source resource '" + p_source_resource + "' already is loading '" + local_path + "'.");
 		}
+	}
 
-		//get ptr
-		Resource **rptr = ResourceCache::resources.getptr(local_path);
+	if (thread_load_tasks.has(local_path)) {
+		thread_load_tasks[local_path].requests++;
+		if (p_source_resource != String()) {
+			thread_load_tasks[p_source_resource].sub_tasks.insert(local_path);
+		}
+		thread_load_mutex->unlock();
+		return OK;
+	}
 
-		if (rptr) {
-			RES res(*rptr);
-			//it is possible this resource was just freed in a thread. If so, this referencing will not work and resource is considered not cached
-			if (res.is_valid()) {
-				//referencing is fine
-				if (r_error)
-					*r_error = OK;
-				if (ResourceCache::lock) {
-					ResourceCache::lock->read_unlock();
+	{
+		//create load task
+
+		ThreadLoadTask load_task;
+
+		load_task.requests = 1;
+		load_task.remapped_path = _path_remap(local_path, &load_task.xl_remapped);
+		load_task.local_path = local_path;
+		load_task.type_hint = p_type_hint;
+		load_task.use_sub_threads = p_use_sub_threads;
+
+		{ //must check if resource is already loaded before attempting to load it in a thread
+
+			if (load_task.loader_id == Thread::get_caller_id()) {
+				thread_load_mutex->unlock();
+				ERR_FAIL_V_MSG(ERR_INVALID_PARAMETER, "Attempted to load a resource already being loaded from this thread, cyclic reference?");
+			}
+			//lock first if possible
+			if (ResourceCache::lock) {
+				ResourceCache::lock->read_lock();
+			}
+
+			//get ptr
+			Resource **rptr = ResourceCache::resources.getptr(local_path);
+
+			if (rptr) {
+				RES res(*rptr);
+				//it is possible this resource was just freed in a thread. If so, this referencing will not work and resource is considered not cached
+				if (res.is_valid()) {
+					//referencing is fine
+					load_task.resource = res;
+					load_task.status = THREAD_LOAD_LOADED;
+					load_task.progress = 1.0;
 				}
-				_remove_from_loading_map(local_path);
-				return res;
+			}
+			if (ResourceCache::lock) {
+				ResourceCache::lock->read_unlock();
 			}
 		}
-		if (ResourceCache::lock) {
-			ResourceCache::lock->read_unlock();
+
+		if (p_source_resource != String()) {
+			thread_load_tasks[p_source_resource].sub_tasks.insert(local_path);
 		}
+
+		thread_load_tasks[local_path] = load_task;
 	}
 
-	bool xl_remapped = false;
-	String path = _path_remap(local_path, &xl_remapped);
+	ThreadLoadTask &load_task = thread_load_tasks[local_path];
 
-	if (path == "") {
-		if (!p_no_cache) {
-			_remove_from_loading_map(local_path);
+	if (load_task.resource.is_null()) { //needs  to be loaded in thread
+
+		load_task.semaphore = memnew(Semaphore);
+		if (thread_loading_count < thread_load_max) {
+			thread_loading_count++;
+			thread_load_semaphore->post(); //we have free threads, so allow one
+		} else {
+			thread_waiting_count++;
 		}
-		ERR_FAIL_V_MSG(RES(), "Remapping '" + local_path + "' failed.");
+
+		print_lt("REQUEST: load count: " + itos(thread_loading_count) + " / wait count: " + itos(thread_waiting_count) + " / suspended count: " + itos(thread_suspended_count) + " / active: " + itos(thread_loading_count - thread_suspended_count));
+
+		load_task.thread = Thread::create(_thread_load_function, &thread_load_tasks[local_path]);
+		load_task.loader_id = load_task.thread->get_id();
 	}
 
-	print_verbose("Loading resource: " + path);
-	RES res = _load(path, local_path, p_type_hint, p_no_cache, r_error);
+	thread_load_mutex->unlock();
+
+	return OK;
+}
+
+float ResourceLoader::_dependency_get_progress(const String &p_path) {
 
-	if (res.is_null()) {
-		if (!p_no_cache) {
-			_remove_from_loading_map(local_path);
+	if (thread_load_tasks.has(p_path)) {
+		ThreadLoadTask &load_task = thread_load_tasks[p_path];
+		int dep_count = load_task.sub_tasks.size();
+		if (dep_count > 0) {
+			float dep_progress = 0;
+			for (Set<String>::Element *E = load_task.sub_tasks.front(); E; E = E->next()) {
+				dep_progress += _dependency_get_progress(E->get());
+			}
+			dep_progress /= float(dep_count);
+			dep_progress *= 0.5;
+			dep_progress += load_task.progress * 0.5;
+			return dep_progress;
+		} else {
+			return load_task.progress;
 		}
-		print_verbose("Failed loading resource: " + path);
-		return RES();
+
+	} else {
+		return 1.0; //assume finished loading it so it no longer exists
 	}
-	if (!p_no_cache)
-		res->set_path(local_path);
+}
 
-	if (xl_remapped)
-		res->set_as_translation_remapped(true);
+ResourceLoader::ThreadLoadStatus ResourceLoader::load_threaded_get_status(const String &p_path, float *r_progress) {
 
-#ifdef TOOLS_ENABLED
+	String local_path;
+	if (p_path.is_rel_path())
+		local_path = "res://" + p_path;
+	else
+		local_path = ProjectSettings::get_singleton()->localize_path(p_path);
 
-	res->set_edited(false);
-	if (timestamp_on_load) {
-		uint64_t mt = FileAccess::get_modified_time(path);
-		//printf("mt %s: %lli\n",remapped_path.utf8().get_data(),mt);
-		res->set_last_modified_time(mt);
+	thread_load_mutex->lock();
+	if (!thread_load_tasks.has(local_path)) {
+		thread_load_mutex->unlock();
+		return THREAD_LOAD_INVALID_RESOURCE;
 	}
-#endif
-
-	if (!p_no_cache) {
-		_remove_from_loading_map(local_path);
+	ThreadLoadTask &load_task = thread_load_tasks[local_path];
+	ThreadLoadStatus status;
+	status = load_task.status;
+	if (r_progress) {
+		*r_progress = _dependency_get_progress(local_path);
 	}
 
-	if (_loaded_callback) {
-		_loaded_callback(res, p_path);
-	}
+	thread_load_mutex->unlock();
 
-	return res;
+	return status;
 }
-
-bool ResourceLoader::exists(const String &p_path, const String &p_type_hint) {
+RES ResourceLoader::load_threaded_get(const String &p_path, Error *r_error) {
 
 	String local_path;
 	if (p_path.is_rel_path())
@@ -424,29 +442,81 @@ bool ResourceLoader::exists(const String &p_path, const String &p_type_hint) {
 	else
 		local_path = ProjectSettings::get_singleton()->localize_path(p_path);
 
-	if (ResourceCache::has(local_path)) {
-
-		return true; // If cached, it probably exists
+	thread_load_mutex->lock();
+	if (!thread_load_tasks.has(local_path)) {
+		thread_load_mutex->unlock();
+		if (r_error) {
+			*r_error = ERR_INVALID_PARAMETER;
+		}
+		return RES();
 	}
 
-	bool xl_remapped = false;
-	String path = _path_remap(local_path, &xl_remapped);
+	ThreadLoadTask &load_task = thread_load_tasks[local_path];
 
-	// Try all loaders and pick the first match for the type hint
-	for (int i = 0; i < loader_count; i++) {
+	//semaphore still exists, meaning its still loading, request poll
+	Semaphore *semaphore = load_task.semaphore;
+	if (semaphore) {
+		load_task.poll_requests++;
 
-		if (!loader[i]->recognize_path(path, p_type_hint)) {
-			continue;
+		{
+			// As we got a semaphore, this means we are going to have to wait
+			// until the sub-resource is done loading
+			//
+			// As this thread will become 'blocked' we should "echange" its
+			// active status with a waiting one, to ensure load continues.
+			//
+			// This ensures loading is never blocked and that is also within
+			// the maximum number of active threads.
+
+			if (thread_waiting_count > 0) {
+				thread_waiting_count--;
+				thread_loading_count++;
+				thread_load_semaphore->post();
+
+				load_task.start_next = false; //do not start next since we are doing it here
+			}
+
+			thread_suspended_count++;
+
+			print_lt("GET: load count: " + itos(thread_loading_count) + " / wait count: " + itos(thread_waiting_count) + " / suspended count: " + itos(thread_suspended_count) + " / active: " + itos(thread_loading_count - thread_suspended_count));
 		}
 
-		if (loader[i]->exists(path))
-			return true;
+		thread_load_mutex->unlock();
+		semaphore->wait();
+		thread_load_mutex->lock();
+
+		thread_suspended_count--;
+
+		if (!thread_load_tasks.has(local_path)) { //may have been erased during unlock and this was always an invalid call
+			thread_load_mutex->unlock();
+			if (r_error) {
+				*r_error = ERR_INVALID_PARAMETER;
+			}
+			return RES();
+		}
 	}
 
-	return false;
+	RES resource = load_task.resource;
+	if (r_error) {
+		*r_error = load_task.error;
+	}
+
+	load_task.requests--;
+
+	if (load_task.requests == 0) {
+		if (load_task.thread) { //thread may not have been used
+			Thread::wait_to_finish(load_task.thread);
+			memdelete(load_task.thread);
+		}
+		thread_load_tasks.erase(local_path);
+	}
+
+	thread_load_mutex->unlock();
+
+	return resource;
 }
 
-Ref<ResourceInteractiveLoader> ResourceLoader::load_interactive(const String &p_path, const String &p_type_hint, bool p_no_cache, Error *r_error) {
+RES ResourceLoader::load(const String &p_path, const String &p_type_hint, bool p_no_cache, Error *r_error) {
 
 	if (r_error)
 		*r_error = ERR_CANT_OPEN;
@@ -459,61 +529,131 @@ Ref<ResourceInteractiveLoader> ResourceLoader::load_interactive(const String &p_
 
 	if (!p_no_cache) {
 
-		bool success = _add_to_loading_map(local_path);
-		ERR_FAIL_COND_V_MSG(!success, RES(), "Resource: '" + local_path + "' is already being loaded. Cyclic reference?");
+		thread_load_mutex->lock();
 
-		if (ResourceCache::has(local_path)) {
+		//Is it already being loaded? poll until done
+		if (thread_load_tasks.has(local_path)) {
+			Error err = load_threaded_request(p_path, p_type_hint);
+			if (err != OK) {
+				if (r_error) {
+					*r_error = err;
+				}
+				return RES();
+			}
+			thread_load_mutex->unlock();
 
-			print_verbose("Loading resource: " + local_path + " (cached)");
-			Ref<Resource> res_cached = ResourceCache::get(local_path);
-			Ref<ResourceInteractiveLoaderDefault> ril = Ref<ResourceInteractiveLoaderDefault>(memnew(ResourceInteractiveLoaderDefault));
+			return load_threaded_get(p_path, r_error);
+		}
 
-			ril->resource = res_cached;
-			ril->path_loading = local_path;
-			ril->path_loading_thread = Thread::get_caller_id();
-			return ril;
+		//Is it cached?
+		if (ResourceCache::lock) {
+			ResourceCache::lock->read_lock();
 		}
-	}
 
-	bool xl_remapped = false;
-	String path = _path_remap(local_path, &xl_remapped);
-	if (path == "") {
-		if (!p_no_cache) {
-			_remove_from_loading_map(local_path);
+		Resource **rptr = ResourceCache::resources.getptr(local_path);
+
+		if (rptr) {
+			RES res(*rptr);
+
+			//it is possible this resource was just freed in a thread. If so, this referencing will not work and resource is considered not cached
+			if (res.is_valid()) {
+				if (ResourceCache::lock) {
+					ResourceCache::lock->read_unlock();
+				}
+				thread_load_mutex->unlock();
+
+				if (r_error) {
+					*r_error = OK;
+				}
+
+				return res; //use cached
+			}
 		}
-		ERR_FAIL_V_MSG(RES(), "Remapping '" + local_path + "' failed.");
-	}
 
-	print_verbose("Loading resource: " + path);
+		if (ResourceCache::lock) {
+			ResourceCache::lock->read_unlock();
+		}
 
-	bool found = false;
-	for (int i = 0; i < loader_count; i++) {
+		//load using task (but this thread)
+		ThreadLoadTask load_task;
 
-		if (!loader[i]->recognize_path(path, p_type_hint))
-			continue;
-		found = true;
-		Ref<ResourceInteractiveLoader> ril = loader[i]->load_interactive(path, local_path, r_error);
-		if (ril.is_null())
-			continue;
-		if (!p_no_cache) {
-			ril->set_local_path(local_path);
-			ril->path_loading = local_path;
-			ril->path_loading_thread = Thread::get_caller_id();
+		load_task.requests = 1;
+		load_task.local_path = local_path;
+		load_task.remapped_path = _path_remap(local_path, &load_task.xl_remapped);
+		load_task.type_hint = p_type_hint;
+		load_task.loader_id = Thread::get_caller_id();
+
+		thread_load_tasks[local_path] = load_task;
+
+		thread_load_mutex->unlock();
+
+		_thread_load_function(&thread_load_tasks[local_path]);
+
+		return load_threaded_get(p_path, r_error);
+
+	} else {
+
+		bool xl_remapped = false;
+		String path = _path_remap(local_path, &xl_remapped);
+
+		if (path == "") {
+			ERR_FAIL_V_MSG(RES(), "Remapping '" + local_path + "' failed.");
+		}
+
+		print_verbose("Loading resource: " + path);
+		float p;
+		RES res = _load(path, local_path, p_type_hint, p_no_cache, r_error, false, &p);
+
+		if (res.is_null()) {
+			print_verbose("Failed loading resource: " + path);
+			return RES();
 		}
 
 		if (xl_remapped)
-			ril->set_translation_remapped(true);
+			res->set_as_translation_remapped(true);
+
+#ifdef TOOLS_ENABLED
+
+		res->set_edited(false);
+		if (timestamp_on_load) {
+			uint64_t mt = FileAccess::get_modified_time(path);
+			//printf("mt %s: %lli\n",remapped_path.utf8().get_data(),mt);
+			res->set_last_modified_time(mt);
+		}
+#endif
 
-		return ril;
+		return res;
 	}
+}
 
-	if (!p_no_cache) {
-		_remove_from_loading_map(local_path);
+bool ResourceLoader::exists(const String &p_path, const String &p_type_hint) {
+
+	String local_path;
+	if (p_path.is_rel_path())
+		local_path = "res://" + p_path;
+	else
+		local_path = ProjectSettings::get_singleton()->localize_path(p_path);
+
+	if (ResourceCache::has(local_path)) {
+
+		return true; // If cached, it probably exists
 	}
 
-	ERR_FAIL_COND_V_MSG(found, Ref<ResourceInteractiveLoader>(), "Failed loading resource: " + path + ".");
+	bool xl_remapped = false;
+	String path = _path_remap(local_path, &xl_remapped);
 
-	ERR_FAIL_V_MSG(Ref<ResourceInteractiveLoader>(), "No loader found for resource: " + path + ".");
+	// Try all loaders and pick the first match for the type hint
+	for (int i = 0; i < loader_count; i++) {
+
+		if (!loader[i]->recognize_path(path, p_type_hint)) {
+			continue;
+		}
+
+		if (loader[i]->exists(path))
+			return true;
+	}
+
+	return false;
 }
 
 void ResourceLoader::add_resource_format_loader(Ref<ResourceFormatLoader> p_format_loader, bool p_at_front) {
@@ -984,20 +1124,19 @@ void ResourceLoader::remove_custom_loaders() {
 	}
 }
 
-Mutex ResourceLoader::loading_map_mutex;
-HashMap<ResourceLoader::LoadingMapKey, int, ResourceLoader::LoadingMapKeyHasher> ResourceLoader::loading_map;
-
 void ResourceLoader::initialize() {
+	thread_load_mutex = memnew(Mutex);
+	thread_load_max = OS::get_singleton()->get_processor_count();
+	thread_loading_count = 0;
+	thread_waiting_count = 0;
+	thread_suspended_count = 0;
+	thread_load_semaphore = memnew(Semaphore);
 }
 
 void ResourceLoader::finalize() {
-#ifndef NO_THREADS
-	const LoadingMapKey *K = NULL;
-	while ((K = loading_map.next(K))) {
-		ERR_PRINT("Exited while resource is being loaded: " + K->path);
-	}
-	loading_map.clear();
-#endif
+
+	memdelete(thread_load_mutex);
+	memdelete(thread_load_semaphore);
 }
 
 ResourceLoadErrorNotify ResourceLoader::err_notify = NULL;
@@ -1009,6 +1148,15 @@ void *ResourceLoader::dep_err_notify_ud = NULL;
 bool ResourceLoader::abort_on_missing_resource = true;
 bool ResourceLoader::timestamp_on_load = false;
 
+Mutex *ResourceLoader::thread_load_mutex = nullptr;
+HashMap<String, ResourceLoader::ThreadLoadTask> ResourceLoader::thread_load_tasks;
+Semaphore *ResourceLoader::thread_load_semaphore = nullptr;
+
+int ResourceLoader::thread_loading_count = 0;
+int ResourceLoader::thread_waiting_count = 0;
+int ResourceLoader::thread_suspended_count = 0;
+int ResourceLoader::thread_load_max = 0;
+
 SelfList<Resource>::List ResourceLoader::remapped_list;
 HashMap<String, Vector<String> > ResourceLoader::translation_remaps;
 HashMap<String, String> ResourceLoader::path_remaps;