C:/knet/include/kNet/WaitFreeQueue.h

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/* Copyright 2010 Jukka Jylänki

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License. */
#pragma once

#include "Alignment.h"

namespace kNet
{


template<typename T>
class WaitFreeQueue
{
public:
   explicit WaitFreeQueue(size_t maxElements)
   :head(0), tail(0)
   {
      assert(IS_POW2(maxElements)); // The caller really needs to round to correct pow2,
      assert(maxElements > 2);
      maxElements = (size_t)RoundUpToNextPow2((u32)maxElements); // but avoid any silliness in release anyways.

      data = new T[maxElements];
      maxElementsMask = maxElements - 1;
   }

   ~WaitFreeQueue()
   {
      delete[] data;
   }

   int Capacity() const { return maxElementsMask; }

   int CapacityLeft() const { return Capacity() - Size(); }

   bool Insert(const T &value)
   {
      // Inserts are made to the 'tail' of the queue, incrementing the tail index.
      unsigned long tail_ = tail;
      unsigned long nextTail = (tail_ + 1) & maxElementsMask;
      if (nextTail == head)
         return false;
      data[tail_] = value;
      tail = nextTail;

      return true;
   }

   void InsertWithResize(const T &value)
   {
      bool success = Insert(value);
      if (!success)
      {
         DoubleCapacity();
         success = Insert(value);
      }
      assert(success);
   }

   void Resize(size_t newSize)
   {
      assert(IS_POW2(newSize)); // The caller really needs to round to correct pow2,
      newSize = (size_t)RoundUpToNextPow2((u32)newSize); // but avoid any silliness in release anyways.

      T *newData = new T[newSize];
      unsigned long newTail = 0;
      for(unsigned long i = 0; i < Size(); ++i)
         newData[newTail++] = *ItemAt(i);
      delete[] data;
      data = newData;
      head = 0;
      tail = newTail;
      maxElementsMask = newSize - 1;
   }

   void DoubleCapacity() { Resize(2*(maxElementsMask+1)); }

   T *Front()
   {
      if (head == tail)
         return 0;
      return &data[head];
   }

   T *ItemAt(int index)
   {
      assert(index < (int)Size());
      return &data[(head + index) & maxElementsMask];
   }

   const T *ItemAt(int index) const
   {
      assert(index < (int)Size());
      return &data[(head + index) & maxElementsMask];
   }

   bool Contains(const T &item) const
   {
      for(int i = 0; i < (int)Size(); ++i)
         if (*ItemAt(i) == item)
            return true;
      return false;
   }

   void EraseItemAt(int index)
   {
      if (index <= Size()>>1)
         EraseItemAtMoveFront(index);
      else
         EraseItemAtMoveBack(index);
   }

   const T *Front() const
   {
      if (head == tail)
         return 0;
      return &data[head];
   }

   T TakeFront()
   {
      T frontVal = *Front();
      PopFront();
      return frontVal;
   }

   void Clear()
   {
      tail = head;
   }

   unsigned long Size() const
   {
      unsigned long head_ = head;
      unsigned long tail_ = tail;
      if (tail_ >= head_)
         return tail_ - head_;
      else
         return maxElementsMask + 1 - (head_ - tail_);
   }

   void PopFront()
   {
      assert(head != tail);
      if (head == tail)
         return;
      size_t head_ = (head + 1) & maxElementsMask;
      head = head_;
   }

private:
   T *data;
   unsigned long maxElementsMask;
   volatile unsigned long head;
   volatile unsigned long tail; 

   WaitFreeQueue(const WaitFreeQueue<T> &rhs);
   void operator=(const WaitFreeQueue<T> &rhs);

   void EraseItemAtMoveFront(int index)
   {
      assert(Size() > 0);
      int numItemsToMove = index;
      for(int i = 0; i < numItemsToMove; ++i)
         data[(head+index + maxElementsMask+1 -i)&maxElementsMask] = data[(head+index + maxElementsMask+1 -i-1) &maxElementsMask];
      head = (head+1) & maxElementsMask;
   }

   void EraseItemAtMoveBack(int index)
   {
      assert(Size() > 0);
      int numItemsToMove = Size()-1-index;
      for(int i = 0; i < numItemsToMove; ++i)
         data[(head+index+i)&maxElementsMask] = data[(head+index+i+1)&maxElementsMask];
      tail = (tail + maxElementsMask+1 - 1) & maxElementsMask;
   }
};

template<typename T>
bool ContainerUniqueAndNoNullElements(const WaitFreeQueue<T> &cont)
{
   for(size_t i = 0; i < cont.Size(); ++i)
      for(size_t j = i+1; j < cont.Size(); ++j)
         if (*cont.ItemAt(i) == *cont.ItemAt(j) || *cont.ItemAt(i) == 0)
            return false;
   return true;
}

} // ~kNet