/* -*- C++ -*-

This file declares the ResourceRestrictionPolicy class.

$ Author: Mirko Boehm $
$ Copyright: (C) 2004, 2005 Mirko Boehm $
$ Contact: mirko@kde.org
http://www.kde.org
http://www.hackerbuero.org $

   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public
   License as published by the Free Software Foundation; either
   version 2 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
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public License
   along with this library; see the file COPYING.LIB.  If not, write to
   the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
   Boston, MA 02110-1301, USA.

$Id: Job.h 32 2005-08-17 08:38:01Z mirko $
*/

#ifndef RESOURCE_RESTRICTION_POLICY_H
#define RESOURCE_RESTRICTION_POLICY_H

#include "QueuePolicy.h"

namespace ThreadWeaver {


    /** ResourceRestrictionPolicy is used to limit the number of concurrent accesses to the same resource.

    If a set of Jobs accesses a resource that can be overloaded, this may
    degrade application performance. For example, loading too many files
    from the hard disc at the same time may lead to longer load times.
    ResourceRestrictionPolicy can be used to cap the number of
    accesses. Resource restriction policies are shared between the
    affected jobs. All jobs that share a resurce restriction policy have
    to acquire permission from the policy before they can run. In this
    way, resource restrictions can be compared to semaphores, only that
    they require no locking at the thread level.

    The SMIV example uses a resource restriction to limit the number of
    images files that are loaded from the disk at the same time.

    */

    class THREADWEAVER_EXPORT ResourceRestrictionPolicy : public QueuePolicy
    {
    public:
        explicit ResourceRestrictionPolicy ( int cap = 0);
        ~ResourceRestrictionPolicy();

        /**
         * Cap the number of simulataniously executing jobs.
         * Capping the amount of jobs will make sure that at max the number of jobs
         * executing at any time is limited to the capped amount.
         * Note that immediately after setting the amount of running jobs may be higher
         * than the set amount. This setting only limits the starting of new jobs.
         * @param newCap the new cap to limit the amount of parallel jobs.
         */
        void setCap (int newCap);
        int cap() const;
        bool canRun( Job* );
        void free (Job*);
        void release (Job*);
        void destructed (Job*);

    private:
        class Private;
        Private* const d;
    };

}

#endif // RESOURCE_RESTRICTION_POLICY_H
