Refactor Node Processing

* Node processing works on the concept of process groups.
* A node group can be inherited, run on main thread, or a sub-thread.
* Groups can be ordered.
* Process priority is now present for physics.

This is the first steps towards implementing https://github.com/godotengine/godot-proposals/issues/6424.
No threading or thread guards exist yet in most of the scene code other than Node. That will have to be added later.

scene/main/scene_tree.h

@@ -33,6 +33,7 @@
 
 #include "core/os/main_loop.h"
 #include "core/os/thread_safe.h"
+#include "core/templates/paged_allocator.h"
 #include "core/templates/self_list.h"
 #include "scene/resources/mesh.h"
 
@@ -86,6 +87,34 @@ public:
 	typedef void (*IdleCallback)();
 
 private:
+	CallQueue::Allocator *process_group_call_queue_allocator = nullptr;
+
+	struct ProcessGroup {
+		CallQueue call_queue;
+		Vector<Node *> nodes;
+		Vector<Node *> physics_nodes;
+		bool node_order_dirty = true;
+		bool physics_node_order_dirty = true;
+		bool removed = false;
+		Node *owner = nullptr;
+		uint64_t last_pass = 0;
+	};
+
+	struct ProcessGroupSort {
+		_FORCE_INLINE_ bool operator()(const ProcessGroup *p_left, const ProcessGroup *p_right) const;
+	};
+
+	PagedAllocator<ProcessGroup, true> group_allocator; // Allocate groups on pages, to enhance cache usage.
+
+	LocalVector<ProcessGroup *> process_groups;
+	bool process_groups_dirty = true;
+	LocalVector<ProcessGroup *> local_process_group_cache; // Used when processing to group what needs to
+	uint64_t process_last_pass = 1;
+
+	ProcessGroup default_process_group;
+
+	bool node_threading_disabled = false;
+
 	struct Group {
 		Vector<Node *> nodes;
 		bool changed = false;
@@ -117,7 +146,7 @@ private:
 	StringName node_renamed_name = "node_renamed";
 
 	int64_t current_frame = 0;
-	int node_count = 0;
+	int nodes_in_tree_count = 0;
 
 #ifdef TOOLS_ENABLED
 	Node *edited_scene_root = nullptr;
@@ -134,8 +163,10 @@ private:
 	};
 
 	// Safety for when a node is deleted while a group is being called.
-	int call_lock = 0;
-	HashSet<Node *> call_skip; // Skip erased nodes.
+
+	bool processing = false;
+	int nodes_removed_on_group_call_lock = 0;
+	HashSet<Node *> nodes_removed_on_group_call; // Skip erased nodes.
 
 	List<ObjectID> delete_queue;
 
@@ -143,7 +174,7 @@ private:
 	bool ugc_locked = false;
 	void _flush_ugc();
 
-	_FORCE_INLINE_ void _update_group_order(Group &g, bool p_use_priority = false);
+	_FORCE_INLINE_ void _update_group_order(Group &g);
 
 	TypedArray<Node> _get_nodes_in_group(const StringName &p_group);
 
@@ -187,7 +218,15 @@ private:
 	void remove_from_group(const StringName &p_group, Node *p_node);
 	void make_group_changed(const StringName &p_group);
 
-	void _notify_group_pause(const StringName &p_group, int p_notification);
+	void _process_group(ProcessGroup *p_group, bool p_physics);
+	void _process_groups_thread(uint32_t p_index, bool p_physics);
+	void _process(bool p_physics);
+
+	void _remove_process_group(Node *p_node);
+	void _add_process_group(Node *p_node);
+	void _remove_node_from_process_group(Node *p_node, Node *p_owner);
+	void _add_node_to_process_group(Node *p_node, Node *p_owner);
+
 	void _call_group_flags(const Variant **p_args, int p_argcount, Callable::CallError &r_error);
 	void _call_group(const Variant **p_args, int p_argcount, Callable::CallError &r_error);
 
@@ -383,6 +422,7 @@ public:
 
 	static void add_idle_callback(IdleCallback p_callback);
 
+	void set_disable_node_threading(bool p_disable);
 	//default texture settings
 
 	SceneTree();