/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */

/*

 * Copyright (c) 2009 INRIA

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation;

 *

 * This program 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 General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 *

 * Author: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>

 */

#ifndef CALENDAR_SCHEDULER_H

#define CALENDAR_SCHEDULER_H

#include "scheduler.h"

#include <stdint.h>

#include <list>

namespace ns3 {

class EventImpl;

/**

 * \ingroup scheduler

 * \brief a calendar queue event scheduler

 *

 * This event scheduler is a direct implementation of the algorithm known as a calendar queue.

 * first published in 1988 in "Calendar Queues: A Fast O(1) Priority Queue Implementation for

 * the Simulation Event Set Problem" by Randy Brown. There are many refinements published

 * later but this class implements the original algorithm (to the best of my knowledge).

 *

 * Note: This queue is much slower than I expected (much slower than the std::map queue)

 * and this seems to be because the original resizing policy is horribly bad. This is

 * most likely the reason why there have been so many variations published which all

 * slightly tweak the resizing heuristics to obtain a better distribution of events

 * across buckets.

 */

class CalendarScheduler : public Scheduler

{

public:

  static TypeId GetTypeId (void);

  CalendarScheduler ();

  virtual ~CalendarScheduler ();

  virtual void Insert (const Event &ev);

  virtual bool IsEmpty (void) const;

  virtual Event PeekNext (void) const;

  virtual Event RemoveNext (void);

  virtual void Remove (const Event &ev);

private:

  void ResizeUp (void);

  void ResizeDown (void);

  void Resize (uint32_t newSize);

  uint32_t CalculateNewWidth (void);

  void Init (uint32_t nBuckets,

             uint64_t width,

             uint64_t startPrio);

  inline uint32_t Hash (uint64_t key) const;

  void PrintInfo (void);

  void DoResize (uint32_t newSize, uint32_t newWidth);

  Scheduler::Event DoRemoveNext (void);

  void DoInsert (const Event &ev);

  typedef std::list<Scheduler::Event> Bucket;

  Bucket *m_buckets;

  // number of buckets in array

  uint32_t m_nBuckets;

  // duration of a bucket

  uint64_t m_width;

  // bucket index from which the last event was dequeued

  uint32_t m_lastBucket;

  // priority at the top of the bucket from which last event was dequeued

  uint64_t m_bucketTop;

  // the priority of the last event removed

  uint64_t m_lastPrio;

  // number of events in queue

  uint32_t m_qSize;

};

} // namespace ns3

#endif /* CALENDAR_SCHEDULER_H */