INVALID_CONTEXT
old_ctx = INVALID_CONTEXT;
if (old_ctx != INVALID_CONTEXT) {
old_ctx = INVALID_CONTEXT;
if (old_ctx != INVALID_CONTEXT) {
old_ctx = INVALID_CONTEXT;
if (old_ctx != INVALID_CONTEXT) {
old_ctx = INVALID_CONTEXT;
if (old_ctx != INVALID_CONTEXT) {