zthr_cancel
(void) zthr_cancel(arc_adjust_zthr);
(void) zthr_cancel(arc_reap_zthr);
zthr_cancel(condense_thread);
zthr_cancel(discard_thread);
extern void zthr_cancel(zthr_t *t);
boolean_t zthr_cancel;
while (!t->zthr_cancel) {
t->zthr_cancel = B_FALSE;
t->zthr_cancel = B_TRUE;
ASSERT(!t->zthr_cancel);
ASSERT(!t->zthr_cancel);
boolean_t cancelled = t->zthr_cancel;