WSharedObjectTicket.h

//---------------------------------------------------------------------------
//
// Project: OpenWalnut ( http://www.openwalnut.org )
//
// Copyright 2009 OpenWalnut Community, BSV@Uni-Leipzig and CNCF@MPI-CBS
// For more information see http://www.openwalnut.org/copying
//
// This file is part of OpenWalnut.
//
// OpenWalnut 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 3 of the License, or
// (at your option) any later version.
//
// OpenWalnut 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 OpenWalnut. If not, see <http://www.gnu.org/licenses/>.
//
//---------------------------------------------------------------------------
 
#ifndef WSHAREDOBJECTTICKET_H
#define WSHAREDOBJECTTICKET_H
 
#include <memory>
#include <shared_mutex>
 
 
#include "WCondition.h"
 
// The shared object class
template < typename T >
class WSharedObject;
 
/**
 * Class which represents granted access to a locked object. It contains a reference to the object and a lock. The lock is freed after the ticket
 * has been destroyed.
 *
 * \note This class does not provide any member to actually get the contained value/instance. This is done in read and write tickets.
 */
template < typename Data >
class WSharedObjectTicket
{
/**
 * The shared object class needs protected access to create new instances.
 */
friend class WSharedObject< Data >;
public:
    /**
     * Destroys the ticket and releases the lock.
     */
    virtual ~WSharedObjectTicket()
    {
        // NOTE: the derived destructor already unlocks.
        if( m_condition )
        {
            m_condition->notify();
        }
    };
 
    /**
     * If called, the unlock will NOT fire the condition. This is useful in some situations if you find out "hey there actually was nothing
     * changed".
     */
    void suppressUnlockCondition()
    {
        m_condition = std::shared_ptr< WCondition >();
    }
 
protected:
    /**
     * Create a new instance. It is protected to avoid someone to create them. It locks the mutex.
     *
     * \param data the data to protect
     * \param mutex the mutex used to lock
     * \param condition a condition that should be fired upon unlock. Can be NULL.
     */
    WSharedObjectTicket( Data& data, std::shared_ptr< std::shared_mutex > mutex, std::shared_ptr< WCondition > condition ): // NOLINT
        m_data( data ),
        m_mutex( mutex ),
        m_condition( condition )
    {
    };
 
    /**
     * The data to which access is allowed by the ticket
     */
    Data& m_data;
 
    /**
     * The mutex used for locking.
     */
    std::shared_ptr< std::shared_mutex > m_mutex;
 
    /**
     * A condition which gets notified after unlocking. Especially useful to notify waiting threads about a change in the object.
     */
    std::shared_ptr< WCondition > m_condition;
 
    /**
     * Unlocks the mutex.
     */
    virtual void unlock() = 0;
 
private:
};
 
#endif  // WSHAREDOBJECTTICKET_H