godot/core/object_rc.h

/*************************************************************************/
/*  object_rc.h                                                          */
/*************************************************************************/
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/*                           GODOT ENGINE                                */
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/* Copyright (c) 2007-2022 Juan Linietsky, Ariel Manzur.                 */
/* Copyright (c) 2014-2022 Godot Engine contributors (cf. AUTHORS.md).   */
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#ifndef OBJECT_RC_H
#define OBJECT_RC_H

#include "core/os/memory.h"
#include "core/typedefs.h"

#include <atomic>

class Object;

// Used to track Variants pointing to a non-Reference Object
class ObjectRC {
	std::atomic<Object *> _ptr;
	std::atomic<uint32_t> _users;

public:
	// This is for allowing debug builds to check for instance ID validity,
	// so warnings are shown in debug builds when a stray Variant (one pointing
	// to a released Object) would have happened.
	const ObjectID instance_id;

	_FORCE_INLINE_ void increment() {
		_users.fetch_add(1, std::memory_order_relaxed);
	}

	_FORCE_INLINE_ bool decrement() {
		return _users.fetch_sub(1, std::memory_order_relaxed) == 1;
	}

	_FORCE_INLINE_ bool invalidate() {
		_ptr.store(nullptr, std::memory_order_release);
		return decrement();
	}

	_FORCE_INLINE_ Object *get_ptr() {
		return _ptr.load(std::memory_order_acquire);
	}

	_FORCE_INLINE_ ObjectRC(Object *p_object) :
			instance_id(p_object->get_instance_id()) {
		// 1 (the Object) + 1 (the first user)
		_users.store(2, std::memory_order_relaxed);
		_ptr.store(p_object, std::memory_order_release);
	}
};

#endif // OBJECT_RC_H