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/*
Copyright (C) 2000-2007 Paul Davis
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., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#ifndef __pbd_rcu_h__
#define __pbd_rcu_h__
#include "boost/shared_ptr.hpp"
#include "glibmm/thread.h"
#include <list>
template<class T>
class RCUManager
{
public:
RCUManager (T* new_rcu_value) {
x.m_rcu_value = new boost::shared_ptr<T> (new_rcu_value);
}
virtual ~RCUManager() { delete x.m_rcu_value; }
boost::shared_ptr<T> reader () const { return *((boost::shared_ptr<T> *) g_atomic_pointer_get (&x.gptr)); }
virtual boost::shared_ptr<T> write_copy () = 0;
virtual bool update (boost::shared_ptr<T> new_value) = 0;
protected:
union {
boost::shared_ptr<T>* m_rcu_value;
mutable volatile gpointer gptr;
} x;
};
template<class T>
class SerializedRCUManager : public RCUManager<T>
{
public:
SerializedRCUManager(T* new_rcu_value)
: RCUManager<T>(new_rcu_value)
{
}
boost::shared_ptr<T> write_copy ()
{
m_lock.lock();
// clean out any dead wood
typename std::list<boost::shared_ptr<T> >::iterator i;
for (i = m_dead_wood.begin(); i != m_dead_wood.end(); ) {
if ((*i).use_count() == 1) {
i = m_dead_wood.erase (i);
} else {
++i;
}
}
// store the current
current_write_old = RCUManager<T>::x.m_rcu_value;
boost::shared_ptr<T> new_copy (new T(**current_write_old));
return new_copy;
}
bool update (boost::shared_ptr<T> new_value)
{
// we hold the lock at this point effectively blocking
// other writers.
boost::shared_ptr<T>* new_spp = new boost::shared_ptr<T> (new_value);
// update, checking that nobody beat us to it
bool ret = g_atomic_pointer_compare_and_exchange (&RCUManager<T>::x.gptr,
(gpointer) current_write_old,
(gpointer) new_spp);
if (ret) {
// successful update : put the old value into dead_wood,
m_dead_wood.push_back (*current_write_old);
// now delete it - this gets rid of the shared_ptr<T> but
// because dead_wood contains another shared_ptr<T> that
// references the same T, the underlying object lives on
delete current_write_old;
}
m_lock.unlock();
return ret;
}
void flush () {
Glib::Mutex::Lock lm (m_lock);
m_dead_wood.clear ();
}
private:
Glib::Mutex m_lock;
boost::shared_ptr<T>* current_write_old;
std::list<boost::shared_ptr<T> > m_dead_wood;
};
template<class T>
class RCUWriter
{
public:
RCUWriter(RCUManager<T>& manager)
: m_manager(manager)
{
m_copy = m_manager.write_copy();
}
~RCUWriter()
{
// we can check here that the refcount of m_copy is 1
if(m_copy.use_count() == 1) {
m_manager.update(m_copy);
} else {
// critical error.
}
}
// or operator boost::shared_ptr<T> ();
boost::shared_ptr<T> get_copy() { return m_copy; }
private:
RCUManager<T>& m_manager;
// preferably this holds a pointer to T
boost::shared_ptr<T> m_copy;
};
#endif /* __pbd_rcu_h__ */
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