- MPI_Group group = request->comm()->group();
- int src_traced = group->rank(request->src());
- int dst_traced = group->rank(request->dst());
+ // Must be taken before Request::wait() since the request may be set to
+ // MPI_REQUEST_NULL by Request::wait!
+ int src = request->comm()->group()->rank(request->src());
+ int dst = request->comm()->group()->rank(request->dst());