code: public <T extends WebCrawler> void startNonBlocking(WebCrawlerFactory<T> crawlerFactory,
                                                          final int numberOfCrawlers) {
          this.start(crawlerFactory, numberOfCrawlers, false);
      }
docs: Start the crawling session and return immediately.
  
  @param crawlerFactory
  factory to create crawlers on demand for each thread
  @param numberOfCrawlers
  the number of concurrent threads that will be contributing in
  this crawling session.
  @param <T> Your class extending WebCrawler