Previous: Building Transfer Functions Up: Data Transfer Functions Next: Automatic Transfer Function Generation

Structures with Local Pointers

CC++ does not define how local pointers are passed between processor objects. While the value of an integer means the same thing in all processor objects, a local pointer is valid only in the processor object in which it was created.

For structures with local pointers, then, the information needs to be packaged in such a way as to enable the reconstruction of the same structure in the other processor object. For instance:


class Vector {
  int length;
  double* elements;
  friend CCVoid& operator<<(CCVoid&,const Vector&);
  friend CCVoid& operator>>(CCVoid&,Vector&);
};

CCVoid& operator<<(CCVoid& v,const Vector& input)
{
  v << input.length;
  for (int i=0; i<input.length; i++)
    v << input.elements[i];
  return v;
}

CCVoid& operator>>(CCVoid& v,Vector& output)
{
  v >> output.length;
  output.elements = new double[output.length];
  for (int i=0; i<output.length; i++) 
    v >> output.elements[i];
  return v;
}

The local pointer is never really transferred. Rather, the elements of the array that it references are sent in an agreed upon order -- from lowest index to highest index -- so that the identical array can be reconstructed remotely. Also notice that no constructor has been defined for type Vector, and thus CC++ will define one automatically.

The problems with transferring local pointers are also present for arrays, and must be dealt with similarly.

paolo@cs.caltech.edu