pf_purge_thread
extern void pf_purge_thread(void *);
sx_sleep(pf_purge_thread, &pf_end_lock, 0, "pftm", pf_purge_thread_period);
wakeup(pf_purge_thread);
error = kproc_create(pf_purge_thread, NULL, &pf_purge_proc, 0, 0, "pf purge");
wakeup_one(pf_purge_thread);