rosaria/Legacy/Aria/include/ArRingQueue.h

/*
Adept MobileRobots Robotics Interface for Applications (ARIA)
Copyright (C) 2004, 2005 ActivMedia Robotics LLC
Copyright (C) 2006, 2007, 2008, 2009, 2010 MobileRobots Inc.
Copyright (C) 2011, 2012, 2013 Adept Technology

     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation; either version 2 of the License, or
     (at your option) any later version.

     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

If you wish to redistribute ARIA under different terms, contact 
Adept MobileRobots for information about a commercial version of ARIA at 
robots@mobilerobots.com or 
Adept MobileRobots, 10 Columbia Drive, Amherst, NH 03031; +1-603-881-7960
*/


#ifndef _AR_RING_QUEUE_H_
#define _AR_RING_QUEUE_H_

#include <iostream>
#include <list>
#include <ariaTypedefs.h>

/** @brief An expanding ring queue. 
 *
 *  It is used to keep a queue with a minimum of allocation and freeing of
 *  heap memory.
 *  The ring queue is implemented using std::list.  The queue starts with an 
 *  initial capacity, but those initial items are considered 'unused'.  Items
 *  are "pushed" into the queue at the "back", and "popped" from the queue at
 *  the "front". pop() and advance_front() will move the front of the queue to 
 *  the next item, creating a new 'unused slot' for future use; advance_back()
 *  changes the next item in the back to a 'used' slot. push() either uses the
 *  next 'unused' slot, or inserts a new item into the std::list.  
 *  When the capacity of the queue is filled, all operations will fail
 *  except push(). Use push() to insert new items in the queue and increase
 *  its capacity.  
 *
 *  @todo Ideally, this class would be fully threadsafe (with occasional or no mutex
 *  locking), but it is not currently.
 *  @todo Optionally allocate several future 'slots' instead of just one.
 *
 *  @ingroup UtilityClasses
 */
template<class T> 
class ArRingQueue {
public:
  /** @param capacity Initial capacity of the ring queue. 
   *  @param init_value Initial value for new, unused items in the queue. 
   *  */
  ArRingQueue(int capacity, T init_value)
    : ring(capacity, init_value), curSize(0), initval(init_value)
  {
    back_it = ring.begin(); 
    front_it = ring.end();// signals empty state
  }


  /** Get an iterator for the front item of the ring queue (the item that would
   * be returned by pop()). If the queue is currently empty, nil() will be
   * returned.
   * 
   * To remove an item from the queue without
   * making a copy with pop(), first check if the queue is empty(). Then  use this 
   * function to get the data. Then call advance_front(). 
   */
  typename std::list<T>::iterator front() {
    if(empty())
      return nil();
    return front_it;
  }

  /** Get an iterator for the back of the queue (the item that would be
   * replaced by push()). This is not the last item in the queue, rather it is the
   * next, unused, "slot".  If the queue is full, an iterator equivalent to that
   * returned by nil() is returned.
   *
   * To add an item to the queue without pushing
   * a copy with push(), first check if the queue is full (in which case you
   * must push() your item). Then use this function to write the data into the
   * next unused 'slot'. Then call advance_back() to advance the back of the queue
   * to your new item. 
   */
  typename std::list<T>::iterator back() {
    if(front_it == back_it)
    {
      //std::cerr << "ArRingQueue: back(): 0-capacity or full, returning nil.\n";
      return nil();
    }
    return back_it;
  }

  /** Advance (pop) the front of the queue. 'Used' size will be decremented.  */
  void advance_front() {
    if(front_it == ring.end())  // initial or  empty state.
      front_it = ring.begin();
    else if(++front_it == ring.end()) 
      front_it = ring.begin();
    if(front_it == back_it) { // it's now empty (not full)
      front_it = ring.end();
      back_it = ring.begin();
    }
    curSize--;
  }

  /** Same as advance_front() */
  void pop_front() { advance_front(); };

  /** Advance the back (an 'empty' push), if the queue is not full.  'Used' size will be incremented.  */
  void advance_back() {
    if(front_it == back_it) // full or 0-capacity
    {
      // debugging:
      /*
      if(empty()) {
        std::cerr << "ArRingQueue: advance_back(): queue is *empty*, can't advance back.\n";
        return;
      }
      std::cerr << "ArRingQueue: advance_back(): queue is full, can't advance back.\n";
      */
      return;
    }
    if(++back_it == ring.end())
      back_it = ring.begin();
    if(front_it == ring.end())
      front_it = ring.begin();  // no longer empty.
    curSize++;
  }

  /** Add an item to the back of the ring queue. If the queue is full, the
   * capacity of the queue will be expanded and the item
   * will be inserted. */
  void push(const T& item) {
    if(full()) {
      // expand
      back_it = ring.insert(back_it, item);
    } else {
      // back is unused, use it
      *back_it = item;
    }
    advance_back();
  }

  /** Same as push() */
  void push_back(const T& item) { push(item); }

  /** Push a new item, but preserve capacity: instead of expanding the queue if
   * full, then the oldest item is replaced and the front is advanced.
   */
  void push_without_expanding(const T& item) {
    if(full())
      advance_front();
    push(item);
  }

  /** Print the current contents of the queue. 
   *  @pynote use printQueue() instead of print() (which is a reserved word in Python)
  */
  void print() {
    for(typename std::list<T>::const_iterator i = ring.begin(); i != ring.end(); i++) {
      if(i == back_it)
        std::cerr << "]";
      if(i == front_it || (i == ring.begin() && front_it == ring.end()) )
        std::cerr << "[";
      std::cerr << (*i) << "," ;
    }
    std::cerr << std::endl;
  }

  /** Get the number of items currently 'used' in the queue. */
  size_t size() {
    return curSize;
  }

  /** Get the current capacity of the queue. */
  size_t capacity() {
    return ring.size();
  }

  /** Return true if the queue is empty (has no 'used' items), false otherwise.  */
  bool empty() {
    return (front_it == ring.end());
  }

  /** Logically clear the queue, resetting to initial empty state, but preserving current
   * capacity, and leaving all contents as they are; the contents are not
   * destroyed, but will be when replaced by new data later. */
  void reset() {
    front_it = ring.end();
    back_it = ring.begin();
    curSize = 0;
  }

  /** Return true if the queue is full, false otherwise. */
  bool full() {
    return (back_it == front_it);
  }

  /** Return an iterator representing an invalid item. Compare to the return
   * values of front(), back(), pop(), etc. */
  typename std::list<T>::iterator nil() {
    return ring.end();
  }

protected:
  std::list<T> ring;
  typename std::list<T>::iterator front_it, back_it;   
  // push to back, pop from front; front will point to first item, 
  // back to one past last. 

  size_t curSize;
  T initval;

};



#endif