refcount.h

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/*
 * This file is part of Ambulant Player, www.ambulantplayer.org.
 *
 * Copyright (C) 2003-2007 Stichting CWI, 
 * Kruislaan 413, 1098 SJ Amsterdam, The Netherlands.
 *
 * Ambulant Player is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * Ambulant Player 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with Ambulant Player; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */

/* 
 * @$Id: refcount.h,v 1.14 2007/02/12 14:14:39 jackjansen Exp $ 
 */
/* 
 * Ref-counted mechanism implementation.
 *
 */
 
#ifndef AMBULANT_LIB_REFCOUNT_H
#define AMBULANT_LIB_REFCOUNT_H

#include "ambulant/config/config.h"

// assert
#include <cassert>

#include "ambulant/lib/mtsync.h"

#ifdef _MSC_VER
#pragma warning(disable : 4251)
#endif

namespace ambulant {

namespace lib {


/// Interface for reference counted objects.
class AMBULANTAPI ref_counted {
  public:
	virtual ~ref_counted(){}

	/// Increment reference count.
	virtual long add_ref() = 0;

	/// Decrement reference count.
	/// Decrements refcount and frees object when refcount goes to 0.
	/// Returns the new refcount.
	virtual long release() = 0;

	/// Return current reference count.
	virtual long get_ref_count() const = 0;
};

/// An atomic counter.
/// Template argument T exposes a critical section interface.
template <class T>
class basic_atomic_count {	
  public:
	explicit basic_atomic_count(long v): m_value(v){}
	
	/// Increment the counter.
	long operator++() {
		m_cs.enter();
		++m_value;
		m_cs.leave();
		return m_value;
	}
	
	/// Decrement the counter.
	long operator--() {
		m_cs.enter();
		--m_value;
		m_cs.leave();
		return m_value;
	}
	
	/// Return the current value of the counter.
	operator long() const {return m_value;}
	
  private:
	basic_atomic_count(basic_atomic_count const &);
	basic_atomic_count & operator=(basic_atomic_count const &);
	long m_value;
	T m_cs;
};

/// An atomic counter using the standard critical_section for locking.
typedef AMBULANTAPI basic_atomic_count<critical_section> atomic_count;

/// An implementation of the ref_counted interface.
/// The ref_counted_obj class maybe used as a mixin for classes
/// implementing ref_counted objects.
/// For example:
/// class active_player : public ref_counted_obj {
///		....
///		No code related with ref counting.
///		Even the m_refcount doesn't have
///		to be initialized in the constructor of active_player 
///		since the base ref_counted_obj does this by default.
///		....
/// };
class AMBULANTAPI ref_counted_obj : virtual public ref_counted {
  public:
	ref_counted_obj()
	:	m_refcount(1) {}
	
	long add_ref() {return ++m_refcount;}

	long release() {
		if(--m_refcount == 0){
			delete this;
			return 0;
		}
		return m_refcount;
	}
	long get_ref_count() const {return m_refcount;}

  protected:
	atomic_count m_refcount;
};

/// A ref_counted wrapper around a normal objects.
/// Converts normal objects to a ref_counted objects.
/// The cost is that you have to get the wrapped object
/// using get_ptr().
/// As all ref_counted objects and this one
/// is created with the operator new.
template<class T>
class auto_ref : public ref_counted_obj {
  public:
	auto_ref(T* ptr = 0) : m_ptr(ptr) {}
	~auto_ref() { delete m_ptr;}
	
    T* get_ptr() { return m_ptr;}
	void set_ptr(T* ptr = 0) {
		if(ptr != m_ptr) delete m_ptr;
		m_ptr = ptr;
	}
  private:
	T* m_ptr;
}; 

/// Save release idiom: 
/// p = release(p); 
/// if p is deleted then p == 0.
template <class T>
static T* release(T *p) {
	if(!p) return p;
	return p->release()?p:0;
}

} // namespace lib
 
} // namespace ambulant

#endif // AMBULANT_LIB_REFCOUNT_H