lockfreefifo.h

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/******************************************************************************
 Copyright (c) 2012-2016 Institut für Nachrichtentechnik, Universität Rostock
 Copyright (c) 2006-2012 Quality & Usability Lab
                         Deutsche Telekom Laboratories, TU Berlin
 
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// https://AudioProcessingFramework.github.io/
 
 
#ifndef APF_LOCKFREEFIFO_H
#define APF_LOCKFREEFIFO_H
 
#include "apf/math.h"  // for next_power_of_2()
#include "apf/misc.h"  // for NonCopyable
#include "apf/container.h"  // for fixed_vector
 
namespace apf
{
 
template<typename T> class LockFreeFifo;  // undefined, use LockFreeFifo<T*>!
 
template<typename T>
class LockFreeFifo<T*> : NonCopyable
{
  public:
    explicit LockFreeFifo(size_t size);
 
    bool push(T* item);
    T* pop();
    bool empty() const;
 
  private:
    volatile size_t _write_index; 
    volatile size_t _read_index;  
    const size_t _size;           
    const size_t _size_mask;      
    fixed_vector<T*> _data;       
};
 
template<typename T>
LockFreeFifo<T*>::LockFreeFifo(size_t size)
  : _write_index(0)
  ,  _read_index(0)
  , _size(apf::math::next_power_of_2(size))
  , _size_mask(_size - 1)
  , _data(_size)
{}
 
template<typename T>
bool
LockFreeFifo<T*>::push(T* item)
{
  if (item == nullptr) return false;
 
  // Concurrent reading and writing is safe for one reader and writer. Once
  // the _read_index is read the _write_index won't change before reading
  // it, because it is modified only in this function. This won't work for
  // multiple readers/writers.
  auto r = _read_index;
  auto w = _write_index;
 
  // Move write pointer by FIFO-size in order to compute the distance to
  // the read pointer in next step.
  if (w < r) w += _size;
 
  // Check if FIFO is full and return false instead of waiting until space is
  // freed. (Prevent read pointer to overtake write pointer.)
  if (w-r > _size-2) return false;
 
  _data[w & _size_mask] = item;
 
  // Set _write_index to next memory location (applying modulo operation)
  _write_index = ++w & _size_mask;
  return true;
}
 
template<typename T>
T*
LockFreeFifo<T*>::pop()
{
  T* retval = nullptr;
 
  if (this->empty()) return retval;
 
  auto r = _read_index;
 
  retval = _data[r];
 
  // Set _read_index to next memory location (applying modulo operation)
  _read_index = ++r & _size_mask;
  return retval;
}
 
template<typename T>
bool
LockFreeFifo<T*>::empty() const
{
  return _read_index == _write_index;
}
 
}  // namespace apf
 
#endif