END blocks in threads

It is possible to add END blocks to threads by using require or eval with the 
appropriate code. These END blocks will then be executed when the thread's 
interpreter is destroyed (i.e., either during a ->join() call, or at program 
termination).

However, calling any the threads manpage methods in such an END block will most 
likely fail (e.g., the application may hang, or generate an error) due to 
mutexes that are needed to control functionality within the the threads 
manpage module.

For this reason, the use of END blocks in threads is strongly discouraged.