LOCK_NB           228 src/dps8/shm.c       rc = flock(fd, LOCK_EX | LOCK_NB);
LOCK_NB           348 src/dps8/shm.c       rc = flock(fd, LOCK_EX | LOCK_NB);
LOCK_NB           290 src/simh/sim_fio.c     rc = flock (fileno(fsc), LOCK_EX | LOCK_NB);