Page.hxx

/*
 * Copyright (C) 2003-2014 The Music Player Daemon Project
 * http://www.musicpd.org
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

/** \file
 *
 * This is a library which manages reference counted buffers.
 */

#ifndef MPD_PAGE_HXX
#define MPD_PAGE_HXX

#include "util/RefCount.hxx"

#include <stddef.h>

/**
 * A dynamically allocated buffer which keeps track of its reference
 * count.  This is useful for passing buffers around, when several
 * instances hold references to one buffer.
 */
class Page {
	/**
	 * The number of references to this buffer.  This library uses
	 * atomic functions to access it, i.e. no locks are required.
	 * As soon as this attribute reaches zero, the buffer is
	 * freed.
	 */
	RefCount ref;

public:
	/**
	 * The size of this buffer in bytes.
	 */
	const size_t size;

	/**
	 * Dynamic array containing the buffer data.
	 */
	unsigned char data[sizeof(long)];

protected:
	Page(size_t _size):size(_size) {}
	~Page() = default;

	/**
	 * Allocates a new #Page object, without filling the data
	 * element.
	 */
	static Page *Create(size_t size);

public:
	/**
	 * Creates a new #page object, and copies data from the
	 * specified buffer.  It is initialized with a reference count
	 * of 1.
	 *
	 * @param data the source buffer
	 * @param size the size of the source buffer
	 */
	static Page *Copy(const void *data, size_t size);

	/**
	 * Concatenates two pages to a new page.
	 *
	 * @param a the first page
	 * @param b the second page, which is appended
	 */
	static Page *Concat(const Page &a, const Page &b);

	/**
	 * Increases the reference counter.
	 */
	void Ref() {
		ref.Increment();
	}

	/**
	 * Decreases the reference counter.  If it reaches zero, the #page is
	 * freed.
	 *
	 * @return true if the #page has been freed
	 */
	bool Unref();
};

#endif