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SessionPool.h

//
// SessionPool.h
//
// $Id: //poco/1.4/Data/include/Poco/Data/SessionPool.h#1 $
//
// Library: Data
// Package: SessionPooling
// Module:  SessionPool
//
// Definition of the SessionPool class.
//
// Copyright (c) 2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// Permission is hereby granted, free of charge, to any person or organization
// obtaining a copy of the software and accompanying documentation covered by
// this license (the "Software") to use, reproduce, display, distribute,
// execute, and transmit the Software, and to prepare derivative works of the
// Software, and to permit third-parties to whom the Software is furnished to
// do so, all subject to the following:
// 
// The copyright notices in the Software and this entire statement, including
// the above license grant, this restriction and the following disclaimer,
// must be included in all copies of the Software, in whole or in part, and
// all derivative works of the Software, unless such copies or derivative
// works are solely in the form of machine-executable object code generated by
// a source language processor.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//


#ifndef Data_SessionPool_INCLUDED
#define Data_SessionPool_INCLUDED


#include "Poco/Data/Data.h"
#include "Poco/Data/PooledSessionHolder.h"
#include "Poco/Data/PooledSessionImpl.h"
#include "Poco/Data/Session.h"
#include "Poco/Timer.h"
#include "Poco/Mutex.h"
#include <list>


namespace Poco {
namespace Data {


00056 class Data_API SessionPool
      /// This class implements session pooling for POCO Data.
      ///
      /// Creating a connection to a database is often a time consuming
      /// operation. Therefore it makes sense to reuse a session object
      /// once it is no longer needed.
      ///
      /// A SessionPool manages a collection of SessionImpl objects 
      /// (decorated with a PooledSessionImpl).
      ///
      /// When a SessionImpl object is requested, the SessionPool first
      /// looks in its set of already initialized SessionImpl for an
      /// available object. If one is found, it is returned to the
      /// client and marked as "in-use". If no SessionImpl is available,
      /// the SessionPool attempts to create a new one for the client.
      /// To avoid excessive creation of SessionImpl objects, a limit
      /// can be set on the maximum number of objects.
      /// Sessions found not to be connected to the database are purged
      /// from the pool whenever one of the following events occurs:
      /// 
      ///   - JanitorTimer event
      ///   - get() request
      ///   - putBack() request
      ///
      /// Not connected idle sessions can not exist.
      ///
      /// Usage example:
      ///
      ///     SessionPool pool("ODBC", "...");
      ///     ...
      ///     Session sess(pool.get());
      ///     ...
{
public:
      SessionPool(const std::string& sessionKey, const std::string& connectionString, int minSessions = 1, int maxSessions = 32, int idleTime = 60);
            /// Creates the SessionPool for sessions with the given sessionKey
            /// and connectionString.
            ///
            /// The pool allows for at most maxSessions sessions to be created.
            /// If a session has been idle for more than idleTime seconds, and more than
            /// minSessions sessions are in the pool, the session is automatically destroyed.
            ///
            /// If idleTime is 0, automatic cleanup of unused sessions is disabled.

      virtual ~SessionPool();
            /// Destroys the SessionPool.
            
      Session get();
            /// Returns a Session.
            ///
            /// If there are unused sessions available, one of the
            /// unused sessions is recycled. Otherwise, a new session
            /// is created. 
            ///
            /// If the maximum number of sessions for this pool has
            /// already been created, a SessionPoolExhaustedException
            /// is thrown.
            
      int capacity() const;
            /// Returns the maximum number of sessions the SessionPool will manage.
            
      int used() const;
            /// Returns the number of sessions currently in use.
            
      int idle() const;
            /// Returns the number of idle sessions.
            
      int dead();
            /// Returns the number of not connected active sessions.

      int allocated() const;
            /// Returns the number of allocated sessions.
            
      int available() const;
            /// Returns the number of available (idle + remaining capacity) sessions.

protected:
      virtual void customizeSession(Session& session);
            /// Can be overridden by subclass to perform custom initialization
            /// of a newly created database session.
            ///
            /// The default implementation does nothing.

00139       typedef Poco::AutoPtr<PooledSessionHolder> PooledSessionHolderPtr;
      typedef Poco::AutoPtr<PooledSessionImpl>   PooledSessionImplPtr;
      typedef std::list<PooledSessionHolderPtr>  SessionList;

      void purgeDeadSessions();
      int deadImpl(SessionList& rSessions);
      void putBack(PooledSessionHolderPtr pHolder);
      void onJanitorTimer(Poco::Timer&);

private:
      SessionPool(const SessionPool&);
      SessionPool& operator = (const SessionPool&);
            
      std::string _sessionKey;
      std::string _connectionString;
      int _minSessions;
      int _maxSessions;
      int _idleTime;
      int _nSessions;
      SessionList _idleSessions;
      SessionList _activeSessions;
      Poco::Timer _janitorTimer;
      mutable Poco::FastMutex _mutex;
      
      friend class PooledSessionImpl;
};


} } // namespace Poco::Data


#endif // Data_SessionPool_INCLUDED

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