// Number of concurrent tasks
        final int numTasks = 100;
        // Interval in milliseconds
        final Long waittime = 100L;

        CrawlingParameterUtil.setUrlQueue(new UrlQueueImpl());
        final UrlQueue q = CrawlingParameterUtil.getUrlQueue();
        for (int i = 0; i < numTasks; i++) {
            q.setUrl("http://example.com");
        }

        // Set a UrlQueue first
        UrlQueue<?> urlQueue = createMockUrlQueue("test", "http://test.com");
        CrawlingParameterUtil.setUrlQueue(urlQueue);
        assertNotNull(CrawlingParameterUtil.getUrlQueue());

        // Set to null
        CrawlingParameterUtil.setUrlQueue(null);

        // Should be null now
        assertNull(CrawlingParameterUtil.getUrlQueue());
    }

                            continue;
                        }

                        startCrawling();

                        // set urlQueue to thread
                        CrawlingParameterUtil.setUrlQueue(urlQueue);

                        if (crawlerContext.intervalController != null) {
                            crawlerContext.intervalController.delay(IntervalController.PRE_PROCESSING);
                        }

  └─ UnsupportedExtractException
```

### Thread-Local Storage

```java
// Set (in CrawlerThread)
CrawlingParameterUtil.setCrawlerContext(context);
CrawlingParameterUtil.setUrlQueue(urlQueue);

// Get (anywhere in same thread)
CrawlerContext ctx = CrawlingParameterUtil.getCrawlerContext();

// Clear (ALWAYS in finally)
CrawlingParameterUtil.clearAll();
```