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_helper_threads.py
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_helper_threads.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.
import logging
import uuid
__all__ = (
'QueueCallbackWorker',
'STOP',
)
_LOGGER = logging.getLogger(__name__)
# Helper thread stop indicator. This could be a sentinel object or None,
# but the sentinel object's ID can change if the process is forked, and
# None has the possibility of a user accidentally killing the helper
# thread.
STOP = uuid.uuid4()
class QueueCallbackWorker(object):
"""A helper that executes a callback for every item in the queue.
Calls a blocking ``get()`` on the ``queue`` until it encounters
:attr:`STOP`.
Args:
queue (~queue.Queue): A Queue instance, appropriate for crossing the
concurrency boundary implemented by ``executor``. Items will
be popped off (with a blocking ``get()``) until :attr:`STOP`
is encountered.
callback (Callable[[str, Dict], Any]): A callback that can process
items pulled off of the queue. Items are assumed to be a pair
of a method name to be invoked and a dictionary of keyword
arguments for that method.
"""
def __init__(self, queue, callback):
self.queue = queue
self._callback = callback
def __call__(self):
while True:
item = self.queue.get()
if item == STOP:
_LOGGER.debug('Exiting the QueueCallbackWorker.')
return
# Run the callback. If any exceptions occur, log them and
# continue.
try:
action, kwargs = item
self._callback(action, kwargs)
except Exception as exc:
_LOGGER.error('%s: %s', exc.__class__.__name__, exc)