This occurs when using SimpleThreadPool.
The run method in the WorkerThread class was changed from this in version 1.8.3:
To this is version 2.0.2:
So now the shutdown method in the WorkerThread class is blocked because is runs in a synchronized block, e.g.
So effectively each worker thread must finish the task it is working on before the shutdown method can proceed to the next worker thread, which prevents Scheduler#shutdown(false) from exiting immediately.