thread_safe_double_buffer.h

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#ifndef NETFT_ETHERCAT_HARDWARE__THREAD_SAFE_DOUBLE_BUFFER
#define NETFT_ETHERCAT_HARDWARE__THREAD_SAFE_DOUBLE_BUFFER

#include <boost/thread/mutex.hpp>

namespace netft_ethercat_hardware
{

template<class T>
class ThreadSafeDoubleBuffer
{
public:
  ThreadSafeDoubleBuffer();
  ThreadSafeDoubleBuffer(const T &initial_value);
  
  void put(const T &value);  
  void get(T &value);  

protected:
  T v1_, v2_;
  boost::mutex mutex1_;
  boost::mutex mutex2_;
  unsigned blocked_counter_;
};


template<class T>  
ThreadSafeDoubleBuffer<T>::ThreadSafeDoubleBuffer() : blocked_counter_(0) 
{ 
  // empty
}

template<class T>  
ThreadSafeDoubleBuffer<T>::ThreadSafeDoubleBuffer(const T &initial_value) : 
  blocked_counter_(0), v1_(initial_value), v2_(initial_value)
{ 
  // empty
}

template<class T>
void ThreadSafeDoubleBuffer<T>::put(const T &value)
{
  // Copy of value into both buffers, only hold lock to one buffer at a time
  { boost::unique_lock<boost::mutex> lock(mutex1_);
    v1_ = value;
  }
  { boost::unique_lock<boost::mutex> lock(mutex2_);
    v2_ = value;
  }
}

template<class T>
void ThreadSafeDoubleBuffer<T>::get(T &value)
{
  // Try getting lock to one of the buffer's
  if (mutex1_.try_lock())
  {
    value = v1_;
    mutex1_.unlock();
    return;
  }
  if (mutex2_.try_lock())
  {
    value = v2_;
    mutex2_.unlock();
    return;
  }
  // OK, block waiting for buffer to open-up
  { boost::unique_lock<boost::mutex> lock(mutex1_);
    v1_ = value;
    ++blocked_counter_;
  }
}    

} //end namespace netft_ethercat_hardware


#endif // NETFT_ETHERCAT_HARDWARE__THREAD_SAFE_DOUBLE_BUFFER