def add_done_callback(self, fn):
"""Add a callback to be executed when the operation is complete.
If the operation is not already complete, this will start a helper
thread to poll for the status of the operation in the background.
Args:
fn (Callable[Future]): The callback to execute when the operation
is complete.
"""
if self._result_set:
_helpers.safe_invoke_callback(fn, self)
return
self._done_callbacks.append(fn)
if self._polling_thread is None:
# The polling thread will exit on its own as soon as the operation
# is done.
self._polling_thread = _helpers.start_daemon_thread(
target=self._blocking_poll)
def _invoke_callbacks(self, *args, **kwargs):
"""Invoke all done callbacks."""
for callback in self._done_callbacks:
_helpers.safe_invoke_callback(callback, *args, **kwargs)
def test_safe_invoke_callback_exception():
callback = mock.Mock(spec=['__call__'], side_effect=ValueError())
result = _helpers.safe_invoke_callback(callback, 'a', b='c')
assert result is None
callback.assert_called_once_with('a', b='c')
def test_safe_invoke_callback():
callback = mock.Mock(spec=['__call__'], return_value=42)
result = _helpers.safe_invoke_callback(callback, 'a', b='c')
assert result == 42
callback.assert_called_once_with('a', b='c')