mapnik/include/mapnik/pool.hpp

/*****************************************************************************
 *
 * This file is part of Mapnik (c++ mapping toolkit)
 *
 * Copyright (C) 2011 Artem Pavlenko
 *
 * This library 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.
 *
 * This library 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 this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 *****************************************************************************/

#ifndef MAPNIK_POOL_HPP
#define MAPNIK_POOL_HPP

// mapnik
#include <mapnik/utils.hpp>

// boost
#include <boost/shared_ptr.hpp>
#include <boost/utility.hpp>
#ifdef MAPNIK_THREADSAFE
#include <boost/thread/mutex.hpp>
#endif

// stl
#include <iostream>
#include <map>
#include <deque>
#include <ctime>

namespace mapnik
{
template <typename T, typename PoolT>
class PoolGuard
{
private:
    const T& obj_;
    PoolT& pool_;
public:
    explicit PoolGuard(const T& ptr,PoolT& pool)
        : obj_(ptr),
          pool_(pool) {}

    ~PoolGuard()
    {
        pool_->returnObject(obj_);
    }

private:
    PoolGuard();
    PoolGuard(const PoolGuard&);
    PoolGuard& operator=(const PoolGuard&);
};

template <typename T,template <typename> class Creator>
class Pool : private boost::noncopyable
{
    typedef boost::shared_ptr<T> HolderType;
    typedef std::deque<HolderType> ContType;

    Creator<T> creator_;
    const unsigned initialSize_;
    const unsigned maxSize_;
    ContType usedPool_;
    ContType unusedPool_;
#ifdef MAPNIK_THREADSAFE
    mutable boost::mutex mutex_;
#endif
public:

    Pool(const Creator<T>& creator,unsigned initialSize=1, unsigned maxSize=10)
        :creator_(creator),
         initialSize_(initialSize),
         maxSize_(maxSize)
    {
        for (unsigned i=0; i < initialSize_; ++i)
        {
            HolderType conn(creator_());
            if (conn->isOK())
                unusedPool_.push_back(conn);
        }
    }

    HolderType borrowObject()
    {
#ifdef MAPNIK_THREADSAFE
        mutex::scoped_lock lock(mutex_);
#endif
        typename ContType::iterator itr=unusedPool_.begin();
        while ( itr!=unusedPool_.end())
        {
#ifdef MAPNIK_DEBUG
            std::clog<<"borrow "<<(*itr).get()<<"\n";
#endif
            if ((*itr)->isOK())
            {
                usedPool_.push_back(*itr);
                unusedPool_.erase(itr);
                return usedPool_[usedPool_.size()-1];
            }
            else
            {
#ifdef MAPNIK_DEBUG
                std::clog<<"bad connection (erase)" << (*itr).get()<<"\n";
#endif
                itr=unusedPool_.erase(itr);
            }
        }
        if (usedPool_.size() < maxSize_)
        {
            HolderType conn(creator_());
            if (conn->isOK())
            {
                usedPool_.push_back(conn);
#ifdef MAPNIK_DEBUG
                std::clog << "create << " << conn.get() << "\n";
#endif
                return conn;
            }
        }
        return HolderType();
    }

    void returnObject(HolderType obj)
    {
#ifdef MAPNIK_THREADSAFE
        mutex::scoped_lock lock(mutex_);
#endif
        typename ContType::iterator itr=usedPool_.begin();
        while (itr != usedPool_.end())
        {
            if (obj.get()==(*itr).get())
            {
#ifdef MAPNIK_DEBUG
                std::clog<<"return "<<(*itr).get()<<"\n";
#endif
                unusedPool_.push_back(*itr);
                usedPool_.erase(itr);
                return;
            }
            ++itr;
        }
    }

    std::pair<unsigned,unsigned> size() const
    {
#ifdef MAPNIK_THREADSAFE
        mutex::scoped_lock lock(mutex_);
#endif
        std::pair<unsigned,unsigned> size(unusedPool_.size(),usedPool_.size());
        return size;
    }
};

}

#endif // MAPNIK_POOL_HPP