Tomcat uses NIO (Non-blocking IO) to keep the connection alive without wasting the waiting threads.

Tomcat 使用 NIO（无阻塞 IO）来保持连接活动，无需浪费等待中的线程。

youdao

Two of the most popular open source servers, Apache Tomcat and Jetty, have both leveraged NIO to add non-blocking IO and thus enable Comet.

两种最流行的开源服务器Apache Tomcat和Jetty都利用NIO增加非阻塞io，从而支持Comet。

youdao