code: def killall(self, wait = None):
          
          with self.tasks.mutex:
              self.tasks.queue.clear()
          self.count_lock.acquire()
          self.kill(self.workers)
          self.count_lock.release()
          self.kill_event.wait(wait)
docs: Kill all active workers.
          @wait: Seconds to wait until last worker ends.
                 If None it waits forever.