ld_threadid_fn
if ((ld)->ld_threadid_fn != NULL) { \
if ((ld)->ld_mutex_threadid[lock] == (ld)->ld_threadid_fn()) { \
(ld)->ld_mutex_threadid[lock] = ld->ld_threadid_fn(); \
if ((ld)->ld_threadid_fn != NULL) { \
if ((ld)->ld_mutex_threadid[lock] == (ld)->ld_threadid_fn()) { \