      size_t clear()
         {
         lock_guard_type<mutex_type> lock(m_mutex);
         size_t count = m_registered_curves.size();
         m_registered_curves.clear();
         return count;
         }
      size_t clear()
         {
         lock_guard_type<mutex_type> lock(m_mutex);
         size_t count = m_registered_curves.size();
         m_registered_curves.clear();
         return count;
         }