source: trunk/packages/vizservers/nanovis/CircularQueue.h @ 2800

/* -*- mode: c++; c-basic-offset: 4; indent-tabs-mode: nil -*- */
/* CircularFifo.h 
* Not any company's property but Public-Domain
* Do with source-code as you will. No requirement to keep this
* header if need to use it/change it/ or do whatever with it
*
* Note that there is No guarantee that this code will work 
* and I take no responsibility for this code and any problems you
* might get if using it. The code is highly platform dependent!
*
* Code & platform dependent issues with it was originally 
* published at http://www.kjellkod.cc/threadsafecircularqueue
* 2009-11-02
* @author Kjell Hedström, hedstrom@kjellkod.cc */

#ifndef CIRCULARFIFO_H_
#define CIRCULARFIFO_H_

/** Circular Fifo (a.k.a. Circular Buffer) 
* Thread safe for one reader, and one writer */
template<typename Element, unsigned int Size>
class CircularFifo {
public:
   enum {Capacity = Size+1};

   CircularFifo() : tail(0), head(0){}
   virtual ~CircularFifo() {}

   bool push(Element& item_);
   bool pop(Element& item_);
   bool isEmpty() const;
   bool isFull() const;
   
   // INSOO
   bool push();
   int tailIndex();
   bool pop();
   bool top(Element&);
   
public:
   volatile unsigned int tail; // input index
   Element array[Capacity];
   volatile unsigned int head; // output index

   unsigned int increment(unsigned int idx_) const;
};




/** Producer only: Adds item to the circular queue. 
* If queue is full at 'push' operation no update/overwrite
* will happen, it is up to the caller to handle this case
*
* \param item_ copy by reference the input item
* \return whether operation was successful or not */
template<typename Element, unsigned int Size>
bool CircularFifo<Element, Size>::push(Element& item_)
{
   int nextTail = increment(tail);
   if(((unsigned int) nextTail) != head)
   {
      array[tail] = item_;
      tail = nextTail;
      return true;
   }

   // queue was full
   return false;
}

template<typename Element, unsigned int Size>
bool CircularFifo<Element, Size>::top(Element& data)
{
   if(head == tail)
      return false;  // empty queue

   data = array[head];
   head = increment(head);
   return true;
}


/** Consumer only: Removes and returns item from the queue
* If queue is empty at 'pop' operation no retrieve will happen
* It is up to the caller to handle this case
*
* \param item_ return by reference the wanted item
* \return whether operation was successful or not */
template<typename Element, unsigned int Size>
bool CircularFifo<Element, Size>::pop(Element& item_)
{
   if(head == tail)
      return false;  // empty queue

   item_ = array[head];
   head = increment(head);
   return true;
}

/** Consumer only: Removes and returns item from the queue
* If queue is empty at 'pop' operation no retrieve will happen
* It is up to the caller to handle this case
*
* \param item_ return by reference the wanted item
* \return whether operation was successful or not */
template<typename Element, unsigned int Size>
bool CircularFifo<Element, Size>::pop()
{
   if(head == tail)
      return false;  // empty queue
   head = increment(head);
   return true;
}

/** Useful for testinng and Consumer check of status
  * Remember that the 'empty' status can change quickly
  * as the Procuder adds more items.
  *
  * \return true if circular buffer is empty */
template<typename Element, unsigned int Size>
bool CircularFifo<Element, Size>::isEmpty() const
{
   return (head == tail);
}

/** Useful for testing and Producer check of status
  * Remember that the 'full' status can change quickly
  * as the Consumer catches up.
  *
  * \return true if circular buffer is full.  */
template<typename Element, unsigned int Size>
bool CircularFifo<Element, Size>::isFull() const
{
   int tailCheck = (tail+1) % Capacity;
   return (((unsigned int) tailCheck) == head);
}

/** Increment helper function for index of the circular queue
* index is inremented or wrapped
*
*  \param idx_ the index to the incremented/wrapped
*  \return new value for the index */
template<typename Element, unsigned int Size>
unsigned int CircularFifo<Element, Size>::increment(unsigned int idx_) const
{
   // increment or wrap
   // =================
   //    index++;
   //    if(index == array.lenght) -> index = 0;
   //
   //or as written below:   
   //    index = (index+1) % array.length
   idx_ = (idx_+1) % Capacity;
   return idx_;
}

template<typename Element, unsigned int Size>
int CircularFifo<Element, Size>::tailIndex()
{
   int nextTail = increment(tail);
   if(((unsigned int)nextTail) != head)
   {
      return tail;
   }

   return -1;
}


template<typename Element, unsigned int Size>
bool CircularFifo<Element, Size>::push()
{
   int nextTail = increment(tail);
   if(((unsigned int)nextTail) != head)
   {
      tail = nextTail;
      return true;
   }

   return false;
}

#endif /* CIRCULARFIFO_H_ */