/
futures.py
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/
futures.py
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# Copyright 2017, Google LLC All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from __future__ import absolute_import
from google.cloud.pubsub_v1 import futures
class StreamingPullFuture(futures.Future):
"""Represents a process that asynchronously performs streaming pull and
schedules messages to be processed.
This future is resolved when the process is stopped (via :meth:`cancel`) or
if it encounters an unrecoverable error. Calling `.result()` will cause
the calling thread to block indefinitely.
"""
def __init__(self, manager):
super(StreamingPullFuture, self).__init__()
self.__manager = manager
self.__manager.add_close_callback(self._on_close_callback)
self.__cancelled = False
def _on_close_callback(self, manager, result):
if self.done():
# The future has already been resolved in a different thread,
# nothing to do on the streaming pull manager shutdown.
return
if result is None:
self.set_result(True)
else:
self.set_exception(result)
def cancel(self):
"""Stops pulling messages and shutdowns the background thread consuming
messages.
"""
# NOTE: We circumvent the base future's self._state to track the cancellation
# state, as this state has different meaning with streaming pull futures.
self.__cancelled = True
return self.__manager.close()
def cancelled(self):
"""
returns:
bool: ``True`` if the subscription has been cancelled.
"""
return self.__cancelled