free memory for matrix in NTL (Number Theory Library)

Question

everyone! I'm using NTL inside the SGX enclave. When I run the application, I got the issue about out of memory. Then I checked the memory, I guess it's due to the heavy use of the NTL matrix.

The basic use of matrix in NTL:

Mat<size_t> mtemp;
mtemp.SetDims(num_row, num_col);

In NTL matrix.cpp, I didn't find any function to free memory.

For kill(), the implementation is about swap():

template<class T>
void Mat<T>::kill()  
{  
   Mat<T> tmp;
   this->swap(tmp);
}  

void swap(Mat& other)
   {
      _mat__rep.swap(other._mat__rep);
      _ntl_swap(_mat__numcols, other._mat__numcols);
   }

template<class T>
void _ntl_swap(T*& a, T*& b)
{
   T* t = a; a = b; b = t;
}

This cannot help free the memory of the matrix. How can I free memory after the use?

Answer 1

The kill() function should do that.
Assuming Mat::~Mat() is implemented to release memory.

template<class T>
void Mat<T>::kill()  
{  
   // This allocates an object with absolute minimum size (probably zero).
   Mat<T> tmp;


   // Now you swap the zero size matrix with your current matrix
   // memory. 
   this->swap(tmp);

   // So your object `this` now holds a zero size matrix.
   // While the object `tmp` holds what used to be in this object.
   // So all the dynamically allocated memory is now inside `tmp`
}
// At this point `tmp` goes out of scope.
// This causes the destructor of `tmp` to be called which
// deallocates the memory that you used to have.
//
// So at this point your object holds a mtrix of zero size.
// and all the old memory has been deallocated.