def _initThreadPool(self):
            """
            Create the threadpool accessible with callFromThread.
            """
            from twisted.python import threadpool
            self.threadpool = threadpool.ThreadPool(
                0, 10, 'twisted.internet.reactor')
            self._threadpoolStartupID = self.callWhenRunning(
                self.threadpool.start)
            self.threadpoolShutdownID = self.addSystemEventTrigger(
                'during', 'shutdown', self._stopThreadPool)

            Create the threadpool accessible with callFromThread.
            
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/base.py