ref_counted.h

/**************************************************************************/
/*  ref_counted.h                                                         */
/**************************************************************************/
/*                         This file is part of:                          */
/*                             GODOT ENGINE                               */
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/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur.                  */
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#pragma once

#include "core/object/class_db.h"
#include "core/templates/safe_refcount.h"

class RefCounted : public Object {
	GDCLASS(RefCounted, Object);
	SafeRefCount refcount;
	SafeRefCount refcount_init;

protected:
	static void _bind_methods();

public:
	_FORCE_INLINE_ bool is_referenced() const { return refcount_init.get() != 1; }
	bool init_ref();
	bool reference(); // returns false if refcount is at zero and didn't get increased
	bool unreference();
	int get_reference_count() const;

	RefCounted();
	~RefCounted() {}
};

template <typename T>
class Ref {
	T *reference = nullptr;

	_FORCE_INLINE_ void ref(const Ref &p_from) {
		ref_pointer<false>(p_from.reference);
	}

	template <bool Init>
	_FORCE_INLINE_ void ref_pointer(T *p_refcounted) {
		if (p_refcounted == reference) {
			return;
		}

		// This will go out of scope and get unref'd.
		Ref cleanup_ref;
		cleanup_ref.reference = reference;
		reference = p_refcounted;
		if (reference) {
			if constexpr (Init) {
				if (!reference->init_ref()) {
					reference = nullptr;
				}
			} else {
				if (!reference->reference()) {
					reference = nullptr;
				}
			}
		}
	}

	//virtual RefCounted * get_reference() const { return reference; }
public:
	static _FORCE_INLINE_ String get_class_static() {
		return T::get_class_static();
	}

	_FORCE_INLINE_ bool operator==(const T *p_ptr) const {
		return reference == p_ptr;
	}
	_FORCE_INLINE_ bool operator!=(const T *p_ptr) const {
		return reference != p_ptr;
	}
#ifdef STRICT_CHECKS
	// Delete these to prevent raw comparisons with `nullptr`.
	bool operator==(std::nullptr_t) const = delete;
	bool operator!=(std::nullptr_t) const = delete;
#endif // STRICT_CHECKS

	_FORCE_INLINE_ bool operator<(const Ref<T> &p_r) const {
		return reference < p_r.reference;
	}
	_FORCE_INLINE_ bool operator==(const Ref<T> &p_r) const {
		return reference == p_r.reference;
	}
	_FORCE_INLINE_ bool operator!=(const Ref<T> &p_r) const {
		return reference != p_r.reference;
	}

	_FORCE_INLINE_ T *operator*() const {
		return reference;
	}

	_FORCE_INLINE_ T *operator->() const {
		return reference;
	}

	_FORCE_INLINE_ T *ptr() const {
		return reference;
	}

	operator Variant() const {
		return Variant(reference);
	}

	void operator=(const Ref &p_from) {
		ref(p_from);
	}

	void operator=(Ref &&p_from) {
		if (reference == p_from.reference) {
			return;
		}
		unref();
		reference = p_from.reference;
		p_from.reference = nullptr;
	}

	template <typename T_Other>
	void operator=(const Ref<T_Other> &p_from) {
		ref_pointer<false>(Object::cast_to<T>(p_from.ptr()));
	}

	void operator=(T *p_from) {
		ref_pointer<true>(p_from);
	}

	void operator=(const Variant &p_variant) {
		Object *object = p_variant.get_validated_object();

		if (object == reference) {
			return;
		}

		ref_pointer<false>(Object::cast_to<T>(object));
	}

	template <typename T_Other>
	void reference_ptr(T_Other *p_ptr) {
		if (reference == p_ptr) {
			return;
		}

		ref_pointer<true>(Object::cast_to<T>(p_ptr));
	}

	Ref(const Ref &p_from) {
		this->operator=(p_from);
	}

	Ref(Ref &&p_from) {
		reference = p_from.reference;
		p_from.reference = nullptr;
	}

	template <typename T_Other>
	Ref(const Ref<T_Other> &p_from) {
		this->operator=(p_from);
	}

	Ref(T *p_from) {
		this->operator=(p_from);
	}

	Ref(const Variant &p_from) {
		this->operator=(p_from);
	}

	inline bool is_valid() const { return reference != nullptr; }
	inline bool is_null() const { return reference == nullptr; }

	void unref() {
		// TODO: this should be moved to mutexes, since this engine does not really
		// do a lot of referencing on references and stuff
		// mutexes will avoid more crashes?

		if (reference) {
			// NOTE: `reinterpret_cast` is "safe" here because we know `T` has simple linear
			// inheritance to `RefCounted`. This guarantees that `T * == `RefCounted *`, which
			// allows us to declare `Ref<T>` with forward declared `T` types.
			if (reinterpret_cast<RefCounted *>(reference)->unreference()) {
				memdelete(reinterpret_cast<RefCounted *>(reference));
			}
			reference = nullptr;
		}
	}

	template <typename... VarArgs>
	void instantiate(VarArgs... p_params) {
		ref(memnew(T(p_params...)));
	}

	Ref() = default;

	~Ref() {
		unref();
	}
};

class WeakRef : public RefCounted {
	GDCLASS(WeakRef, RefCounted);

	ObjectID ref;

protected:
	static void _bind_methods();

public:
	Variant get_ref() const;
	void set_obj(Object *p_object);
	void set_ref(const Ref<RefCounted> &p_ref);

	WeakRef() {}
};

template <typename T>
struct PtrToArg<Ref<T>> {
	_FORCE_INLINE_ static Ref<T> convert(const void *p_ptr) {
		if (p_ptr == nullptr) {
			return Ref<T>();
		}
		// p_ptr points to a RefCounted object
		return Ref<T>(*reinterpret_cast<T *const *>(p_ptr));
	}

	typedef Ref<T> EncodeT;

	_FORCE_INLINE_ static void encode(Ref<T> p_val, const void *p_ptr) {
		// p_ptr points to an EncodeT object which is a Ref<T> object.
		*(const_cast<Ref<RefCounted> *>(reinterpret_cast<const Ref<RefCounted> *>(p_ptr))) = p_val;
	}
};

template <typename T>
struct GetTypeInfo<Ref<T>> {
	static const Variant::Type VARIANT_TYPE = Variant::OBJECT;
	static const GodotTypeInfo::Metadata METADATA = GodotTypeInfo::METADATA_NONE;

	static inline PropertyInfo get_class_info() {
		return PropertyInfo(Variant::OBJECT, String(), PROPERTY_HINT_RESOURCE_TYPE, T::get_class_static());
	}
};

template <typename T>
struct VariantInternalAccessor<Ref<T>> {
	static _FORCE_INLINE_ Ref<T> get(const Variant *v) { return Ref<T>(*VariantInternal::get_object(v)); }
	static _FORCE_INLINE_ void set(Variant *v, const Ref<T> &p_ref) { VariantInternal::object_assign(v, p_ref); }
};

// Zero-constructing Ref initializes reference to nullptr (and thus empty).
template <typename T>
struct is_zero_constructible<Ref<T>> : std::true_type {};

template <typename T>
Ref<T> ObjectDB::get_ref(ObjectID p_instance_id) {
	return Ref<T>(get_instance(p_instance_id));
}