* bpo-37193: remove the thread which finished process request from threads list
* rename variable t to thread.
* don't remove thread from list if it is daemon.
* use lock to protect self._threads.
* use finally block in case of exception from shutdown_request().
* check "not thread.daemon" before lock to avoid holding the lock if it's unnecessary.
* fix the place of _threads_lock.
* separate code to remove a current thread into a function.
* check ValueError when removing thread.
* fix wrong code which all instance shared same lock.
* Extract thread management into a _Threads class to encapsulate atomic operations and separate concerns.
* Replace multiple references of 'block_on_close' with one, avoiding the possibility that 'block_on_close' could change during the course of processing requests. Now, there's exactly one _threads object with behavior fixed for the duration.
* Add docstrings to private classes.
* Add test to ensure that a ThreadingTCPServer can be closed without serving any requests.
* Use _NoThreads as the default value. Fixes AttributeError when server is closed without serving any requests.
* Add blurb
* Add test capturing failure.
Co-authored-by: Jason R. Coombs <jaraco@jaraco.com>
Jason R. Coombs
MARUYAMA Norihiro