Address data races with 'a', 'b', 'c', 'd', 'e', 'counter', 'done', 'nevents', 'nsdevents', 'all_done', and 'eventcnt'. Add isc_mutex_init/isc_mutex_destroy.
Address data races with 'a', 'b', 'c', 'd', 'e', 'counter', 'done', 'nevents', 'nsdevents', 'all_done', and 'eventcnt'. Add isc_mutex_init/isc_mutex_destroy.