Implement multi_threaded implementation in Iterator

src/ifcconvert/IfcConvert.cpp

@@ -218,9 +218,13 @@ int main(int argc, char** argv) {
 	ifc_options.add_options()
 		("calculate-quantities", "Calculate or fix the physical quantity definitions "
 			"based on an interpretation of the geometry when exporting IFC");
+
+	size_t num_threads;
     
 	po::options_description geom_options("Geometry options");
 	geom_options.add_options()
+		("threads,j", po::value<size_t>(&num_threads)->default_value(1),
+			"Number of parallel processing threads for geometry interpretation.")
 		("plan",
 			"Specifies whether to include curves in the output result. Typically "
 			"these are representations of type Plan or Axis. Excluded by default.")
@@ -730,7 +734,7 @@ int main(int argc, char** argv) {
         return EXIT_FAILURE;
     }
 
-    IfcGeom::Iterator<real_t> context_iterator(settings, ifc_file, filter_funcs);
+    IfcGeom::Iterator<real_t> context_iterator(settings, ifc_file, filter_funcs, num_threads);
     if (!context_iterator.initialize()) {
         /// @todo It would be nice to know and print separate error prints for a case where we found no entities
         /// and for a case we found no entities that satisfy our filtering criteria.