cpool.h

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/***********************************************************************
 Copyright (c) 2007-2008 by Educational Technology Resources, Inc. and
 (c) 2007 by Jonathan Wakely.  Others may also hold copyrights on
 code in this file.  See the CREDITS file in the top directory of
 the distribution for details.

 This file is part of MySQL++.

 MySQL++ 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.

 MySQL++ 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 MySQL++; if not, write to the Free Software
 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
 USA
***********************************************************************/

#if !defined(MYSQLPP_CPOOL_H)
#define MYSQLPP_CPOOL_H

#include "beemutex.h"

#include <list>

#include <assert.h>
#include <time.h>

namespace mysqlpp {

#if !defined(DOXYGEN_IGNORE)
// Make Doxygen ignore this
class MYSQLPP_EXPORT Connection;
#endif


class MYSQLPP_EXPORT ConnectionPool
{
public:
        ConnectionPool() { }

        virtual ~ConnectionPool() { assert(empty()); }

        bool empty() const { return pool_.empty(); }

        Connection* grab();

        void release(const Connection* pc);

        void shrink() { clear(false); }

protected:
        void clear(bool all = true);

        virtual Connection* create() = 0;

        virtual void destroy(Connection*) = 0;

        virtual unsigned int max_idle_time() = 0;

private:
        struct ConnectionInfo {
                Connection* conn;
                time_t last_used;
                bool in_use;

                ConnectionInfo(Connection* c) :
                conn(c),
                last_used(time(0)),
                in_use(true)
                {
                }

                // Strict weak ordering for ConnectionInfo objects.
                // 
                // This ordering defines all in-use connections to be "less
                // than" those not in use.  Within each group, connections
                // less recently touched are less than those more recent.
                bool operator<(const ConnectionInfo& rhs) const
                {
                        const ConnectionInfo& lhs = *this;
                        return lhs.in_use == rhs.in_use ?
                                        lhs.last_used < rhs.last_used :
                                        lhs.in_use;
                }
        };
        typedef std::list<ConnectionInfo> PoolT;
        typedef PoolT::iterator PoolIt;

        Connection* find_mru();
        void remove_old_connections();

        PoolT pool_;
        BeecryptMutex mutex_;
};

} // end namespace mysqlpp

#endif // !defined(MYSQLPP_CPOOL_H)

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