Which materialized views are being refreshed?

This is a handy little bit of SQL to see which materialized views are currently being refreshed.

select
      o.owner         "Owner"
     ,o.object_name   "Mat View"
     ,s.username
     ,s.sid           "Sid"
from
     v$lock           l
    ,dba_objects      o
    ,v$session        s
where o.object_id   = l.id1
and   l.type        = 'JI'
and   l.lmode       = 6
and   s.sid         = l.sid
and   o.object_type = 'TABLE';

The trick is in the lock type - JI.