jcomeau@tektonic:~$ grep -C2 -i spin /usr/include/bits/posix_opt.h #define _POSIX_TIMEOUTS 200112L /* We support spinlocks. */ //#define _POSIX_SPIN_LOCKS 200112L /* No we don't */ #define _POSIX_SPIN_LOCKS -1 /* The `spawn' function family is supported. */