code: def _process_callbacks(self):
          
          # Flush all the pipe content.
          os.read(self._schedule_pipe[0], 1024)
  
          # Process calls from executor.
          calls_from_executor, self._calls_from_executor = self._calls_from_executor, []
          for c in calls_from_executor:
              c()
docs: Process callbacks from `call_from_executor` in eventloop.