_BLOCKCOUNT_WAITERS_FLAG
if (atomic_cmpset_int(&bc->__count, _BLOCKCOUNT_WAITERS_FLAG, 0))
old | _BLOCKCOUNT_WAITERS_FLAG));
#define _BLOCKCOUNT_COUNT(c) ((c) & ~_BLOCKCOUNT_WAITERS_FLAG)
#define _BLOCKCOUNT_WAITERS(c) (((c) & _BLOCKCOUNT_WAITERS_FLAG) != 0)