Use multiple threads to import.

- For now everything imports multithreaded by default (should work I guess, let's test).
- Controllable per importer

Early test benchmark. 64 large textures (importing as lossless, _not_ as vram) on a mobile i7, 12 threads:
Importing goes down from 46 to 7 seconds.

For VRAM I will change the logic to use a compressing thread in a subsequent PR, as well as implementing Betsy.

core/io/resource_importer.cpp

@@ -192,6 +192,34 @@ bool ResourceFormatImporter::recognize_path(const String &p_path, const String &
 	return FileAccess::exists(p_path + ".import");
 }
 
+Error ResourceFormatImporter::get_import_order_threads_and_importer(const String &p_path, int &r_order, bool &r_can_threads, String &r_importer) const {
+	r_order = 0;
+	r_importer = "";
+
+	r_can_threads = false;
+	Ref<ResourceImporter> importer;
+
+	if (FileAccess::exists(p_path + ".import")) {
+		PathAndType pat;
+		Error err = _get_path_and_type(p_path, pat);
+
+		if (err == OK) {
+			importer = get_importer_by_name(pat.importer);
+		}
+	} else {
+		importer = get_importer_by_extension(p_path.get_extension().to_lower());
+	}
+
+	if (importer.is_valid()) {
+		r_order = importer->get_import_order();
+		r_importer = importer->get_importer_name();
+		r_can_threads = importer->can_import_threaded();
+		return OK;
+	} else {
+		return ERR_INVALID_PARAMETER;
+	}
+}
+
 int ResourceFormatImporter::get_import_order(const String &p_path) const {
 	Ref<ResourceImporter> importer;
 

core/io/resource_importer.h

@@ -72,6 +72,8 @@ public:
 
 	virtual int get_import_order(const String &p_path) const;
 
+	Error get_import_order_threads_and_importer(const String &p_path, int &r_order, bool &r_can_threads, String &r_importer) const;
+
 	String get_internal_resource_path(const String &p_path) const;
 	void get_internal_resource_path_list(const String &p_path, List<String> *r_paths);
 
@@ -126,6 +128,9 @@ public:
 	virtual String get_option_group_file() const { return String(); }
 
 	virtual Error import(const String &p_source_file, const String &p_save_path, const Map<StringName, Variant> &p_options, List<String> *r_platform_variants, List<String> *r_gen_files = nullptr, Variant *r_metadata = nullptr) = 0;
+	virtual bool can_import_threaded() const { return true; }
+	virtual void import_threaded_begin() {}
+	virtual void import_threaded_end() {}
 
 	virtual Error import_group_file(const String &p_group_file, const Map<String, Map<StringName, Variant>> &p_source_file_options, const Map<String, String> &p_base_paths) { return ERR_UNAVAILABLE; }
 	virtual bool are_import_settings_valid(const String &p_path) const { return true; }

core/templates/thread_work_pool.h

@@ -83,7 +83,7 @@ public:
 		ERR_FAIL_COND(!threads); //never initialized
 		ERR_FAIL_COND(current_work != nullptr);
 
-		index.store(0);
+		index.store(0, std::memory_order_release);
 
 		Work<C, M, U> *w = memnew((Work<C, M, U>));
 		w->instance = p_instance;
@@ -104,8 +104,15 @@ public:
 		return current_work != nullptr;
 	}
 
+	bool is_done_dispatching() const {
+		ERR_FAIL_COND_V(current_work == nullptr, false);
+		return index.load(std::memory_order_acquire) >= current_work->max_elements;
+	}
+
 	uint32_t get_work_index() const {
-		return index;
+		ERR_FAIL_COND_V(current_work == nullptr, 0);
+		uint32_t idx = index.load(std::memory_order_acquire);
+		return MIN(idx, current_work->max_elements);
 	}
 
 	void end_work() {

editor/editor_file_system.cpp

@@ -1922,6 +1922,11 @@ void EditorFileSystem::reimport_file_with_custom_parameters(const String &p_file
 	_reimport_file(p_file, &p_custom_params, p_importer);
 }
 
+void EditorFileSystem::_reimport_thread(uint32_t p_index, ImportThreadData *p_import_data) {
+	p_import_data->max_index = MAX(p_import_data->reimport_from + int(p_index), p_import_data->max_index);
+	_reimport_file(p_import_data->reimport_files[p_import_data->reimport_from + p_index].path);
+}
+
 void EditorFileSystem::reimport_files(const Vector<String> &p_files) {
 	{
 		// Ensure that ProjectSettings::IMPORTED_FILES_PATH exists.
@@ -1939,7 +1944,8 @@ void EditorFileSystem::reimport_files(const Vector<String> &p_files) {
 	importing = true;
 	EditorProgress pr("reimport", TTR("(Re)Importing Assets"), p_files.size());
 
-	Vector<ImportFile> files;
+	Vector<ImportFile> reimport_files;
+
 	Set<String> groups_to_reimport;
 
 	for (int i = 0; i < p_files.size(); i++) {
@@ -1957,8 +1963,8 @@ void EditorFileSystem::reimport_files(const Vector<String> &p_files) {
 			//it's a regular file
 			ImportFile ifile;
 			ifile.path = p_files[i];
-			ifile.order = ResourceFormatImporter::get_singleton()->get_import_order(p_files[i]);
-			files.push_back(ifile);
+			ResourceFormatImporter::get_singleton()->get_import_order_threads_and_importer(p_files[i], ifile.order, ifile.threaded, ifile.importer);
+			reimport_files.push_back(ifile);
 		}
 
 		//group may have changed, so also update group reference
@@ -1969,11 +1975,51 @@ void EditorFileSystem::reimport_files(const Vector<String> &p_files) {
 		}
 	}
 
-	files.sort();
+	reimport_files.sort();
 
-	for (int i = 0; i < files.size(); i++) {
-		pr.step(files[i].path.get_file(), i);
-		_reimport_file(files[i].path);
+	bool use_threads = GLOBAL_GET("editor/import/use_multiple_threads");
+
+	int from = 0;
+	for (int i = 0; i < reimport_files.size(); i++) {
+		if (use_threads && reimport_files[i].threaded) {
+			if (i + 1 == reimport_files.size() || reimport_files[i + 1].importer != reimport_files[from].importer) {
+				if (from - i == 0) {
+					//single file, do not use threads
+					pr.step(reimport_files[i].path.get_file(), i);
+					_reimport_file(reimport_files[i].path);
+				} else {
+					Ref<ResourceImporter> importer = ResourceFormatImporter::get_singleton()->get_importer_by_name(reimport_files[from].importer);
+					ERR_CONTINUE(!importer.is_valid());
+
+					importer->import_threaded_begin();
+
+					ImportThreadData data;
+					data.max_index = from;
+					data.reimport_from = from;
+					data.reimport_files = reimport_files.ptr();
+
+					import_threads.begin_work(i - from + 1, this, &EditorFileSystem::_reimport_thread, &data);
+					int current_index = from - 1;
+					do {
+						if (current_index < data.max_index) {
+							current_index = data.max_index;
+							pr.step(reimport_files[current_index].path.get_file(), current_index);
+						}
+						OS::get_singleton()->delay_usec(1);
+					} while (!import_threads.is_done_dispatching());
+
+					import_threads.end_work();
+
+					importer->import_threaded_end();
+				}
+
+				from = i + 1;
+			}
+
+		} else {
+			pr.step(reimport_files[i].path.get_file(), i);
+			_reimport_file(reimport_files[i].path);
+		}
 	}
 
 	//reimport groups
@@ -2111,7 +2157,7 @@ void EditorFileSystem::_update_extensions() {
 EditorFileSystem::EditorFileSystem() {
 	ResourceLoader::import = _resource_import;
 	reimport_on_missing_imported_files = GLOBAL_DEF("editor/import/reimport_missing_imported_files", true);
-
+	GLOBAL_DEF("editor/import/use_multiple_threads", true);
 	singleton = this;
 	filesystem = memnew(EditorFileSystemDirectory); //like, empty
 	filesystem->parent = nullptr;
@@ -2138,7 +2184,9 @@ EditorFileSystem::EditorFileSystem() {
 	first_scan = true;
 	scan_changes_pending = false;
 	revalidate_import_files = false;
+	import_threads.init();
 }
 
 EditorFileSystem::~EditorFileSystem() {
+	import_threads.finish();
 }

editor/editor_file_system.h

@@ -36,7 +36,9 @@
 #include "core/os/thread_safe.h"
 #include "core/templates/safe_refcount.h"
 #include "core/templates/set.h"
+#include "core/templates/thread_work_pool.h"
 #include "scene/main/node.h"
+
 class FileAccess;
 
 struct EditorProgressBG;
@@ -214,9 +216,11 @@ class EditorFileSystem : public Node {
 
 	struct ImportFile {
 		String path;
+		String importer;
+		bool threaded = false;
 		int order = 0;
 		bool operator<(const ImportFile &p_if) const {
-			return order < p_if.order;
+			return order == p_if.order ? (importer < p_if.importer) : (order < p_if.order);
 		}
 	};
 
@@ -236,6 +240,16 @@ class EditorFileSystem : public Node {
 
 	Set<String> group_file_cache;
 
+	ThreadWorkPool import_threads;
+
+	struct ImportThreadData {
+		const ImportFile *reimport_files;
+		int reimport_from;
+		int max_index = 0;
+	};
+
+	void _reimport_thread(uint32_t p_index, ImportThreadData *p_import_data);
+
 protected:
 	void _notification(int p_what);
 	static void _bind_methods();

editor/import/resource_importer_scene.h

@@ -173,6 +173,8 @@ public:
 	virtual bool has_advanced_options() const override;
 	virtual void show_advanced_options(const String &p_path) override;
 
+	virtual bool can_import_threaded() const override { return false; }
+
 	ResourceImporterScene();
 };
 

scene/3d/gpu_particles_collision_3d.cpp

@@ -346,7 +346,7 @@ void GPUParticlesCollisionSDF::_compute_sdf(ComputeSDFParams *params) {
 	ThreadWorkPool work_pool;
 	work_pool.init();
 	work_pool.begin_work(params->size.z, this, &GPUParticlesCollisionSDF::_compute_sdf_z, params);
-	while (work_pool.get_work_index() < (uint32_t)params->size.z) {
+	while (!work_pool.is_done_dispatching()) {
 		OS::get_singleton()->delay_usec(10000);
 		bake_step_function(work_pool.get_work_index() * 100 / params->size.z, "Baking SDF");
 	}