*     visited.add(uri);
 *     for (Uri newUri : newUris) {
 *       if (!visited.contains(newUri)) { toCrawl.add(newUri); }
 *     }
 *   }
 *
 *   protected void shutDown() throws Exception {
 *     saveUris(toCrawl);
 *   }
 *
 *   protected Scheduler scheduler() {
 *     return Scheduler.newFixedRateSchedule(0, 1, TimeUnit.SECONDS);
 *   }
 * }
 * }</pre>
 *