Quartz scheduler always output the following log when shutdown:

INFO [org.quartz.simpl.SimpleThreadPool] There are still XX worker threads active. See javadoc runInThread(Runnable) for a possible explanation

The thread count XX is not Quartz worker threads. Quarts is using "main" thread group because SimpleThreadPool#isThreadsInheritGroupOfInitializingThread() == true. This is confusing.