grpc and gevent thread pool executor

checkin.py

class ThreadPoolExecutor(concurrent.futures.ThreadPoolExecutor):
     """
     A version of :class:`concurrent.futures.ThreadPoolExecutor` that
     always uses native threads, even when threading is monkey-patched.

     .. versionadded:: 1.2a1
     """

     def __init__(self, max_workers):
         super(ThreadPoolExecutor, self).__init__(max_workers)
         self._threadpool = ThreadPool(max_workers)

     def submit(self, fn, *args, **kwargs):
         future = super(ThreadPoolExecutor, self).submit(fn, *args, **kwargs)
         with self._shutdown_lock:
             work_item = self._work_queue.get()
             assert work_item.fn is fn

         self._threadpool.spawn(work_item.run)
         return future

     def shutdown(self, wait=True):
         super(ThreadPoolExecutor, self).shutdown(wait)
         self._threadpool.kill()

     kill = shutdown # greentest compat

     def _adjust_thread_count(self):
         # Does nothing. We don't want to spawn any "threads",
         # let the threadpool handle that.
         pass