genode/repos/ports/src/noux/shared_pointer.h

/*
 * \brief  Reference-counting smart pointer
 * \author Norman Feske
 * \date   2011-02-17
 */

/*
 * Copyright (C) 2011-2017 Genode Labs GmbH
 *
 * This file is part of the Genode OS framework, which is distributed
 * under the terms of the GNU Affero General Public License version 3.
 */

#ifndef _NOUX__SHARED_POINTER_PTR_H_
#define _NOUX__SHARED_POINTER_PTR_H_

/* Genode includes */
#include <base/lock.h>
#include <base/allocator.h>
#include <base/log.h>

/* Noux includes */
#include <noux_session/sysio.h>

namespace Noux {
	class Reference_counter;
	class Shared_pointer_base;
	template <typename T> class Shared_pointer;
}


class Noux::Reference_counter
{
	private:

		Lock _lock { };
		long _value;

		friend class Shared_pointer_base;

		void _inc_ref_count()
		{
			Lock::Guard guard(_lock);
			_value++;
		}

		/**
		 * \return reference counter after decrement
		 */
		long _dec_ref_count()
		{
			Lock::Guard guard(_lock);
			return --_value;
		}

	public:

		Reference_counter() : _value(0) { }
};


class Noux::Shared_pointer_base
{
	protected:

		Reference_counter *_ref_counter;

		Shared_pointer_base(Reference_counter *ref_counter)
		: _ref_counter(ref_counter) { }

		void _inc_ref_count() {
			if (_ref_counter) _ref_counter->_inc_ref_count(); }

		bool _dec_ref_count() {
			return _ref_counter && (_ref_counter->_dec_ref_count() == 0); }

		long count() const { return _ref_counter ? _ref_counter->_value : -99; }
};


template <typename T>
class Noux::Shared_pointer : public Shared_pointer_base
{
	private:

		T         *_ptr;
		Allocator *_alloc;

		void _dec_ref_count()
		{
			if (Shared_pointer_base::_dec_ref_count()) {

				destroy(_alloc, _ptr);
				_ptr         = 0;
				_alloc       = 0;
				_ref_counter = 0;
			}
		}

	public:

		Shared_pointer() : Shared_pointer_base(0), _ptr(0), _alloc(0) { }

		Shared_pointer(T *ptr, Allocator &alloc)
		: Shared_pointer_base(ptr), _ptr(ptr), _alloc(&alloc)
		{
			_inc_ref_count();
		}

		Shared_pointer(Shared_pointer const & from)
		:
			Shared_pointer_base(from._ref_counter),
			_ptr(from._ptr), _alloc(from._alloc)
		{
			_inc_ref_count();
		}

		Shared_pointer & operator=(const Shared_pointer& from)
		{
			/* check for self assignment */
			if (_ptr == from._ptr)
				return *this;

			/* forget about original pointed-to object */
			_dec_ref_count();

			_ref_counter = from._ref_counter;
			_ptr         = from._ptr;
			_alloc       = from._alloc;

			/* account for newly assigned pointed-to object */
			_inc_ref_count();

			return *this;
		}

		~Shared_pointer()
		{
			_dec_ref_count();
		}

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

		operator bool () const { return _ptr != 0; }

		bool operator== (const Shared_pointer &other)
		{
			return (_ptr == other._ptr);
		}

		template<typename To>
		Shared_pointer<To> dynamic_pointer_cast()
		{
			return Shared_pointer<To>(dynamic_cast<To *>(_ptr), _alloc);
		}
};

#endif /* _NOUX__SHARED_POINTER_H_ */