coordinator.py

# Copyright (c) 2017-present, Facebook, Inc.
#
# 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.
##############################################################################

"""Coordinated access to a shared multithreading/processing queue."""

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from __future__ import unicode_literals

import contextlib
import logging
import threading
import traceback
from six.moves import queue as Queue

log = logging.getLogger(__name__)


class Coordinator(object):

    def __init__(self):
        self._event = threading.Event()

    def request_stop(self):
        log.debug('Coordinator stopping')
        self._event.set()

    def should_stop(self):
        return self._event.is_set()

    def wait_for_stop(self):
        return self._event.wait()

    @contextlib.contextmanager
    def stop_on_exception(self):
        try:
            yield
        except Exception:
            if not self.should_stop():
                traceback.print_exc()
                self.request_stop()


def coordinated_get(coordinator, queue):
    while not coordinator.should_stop():
        try:
            return queue.get(block=True, timeout=1.0)
        except Queue.Empty:
            continue
    raise Exception('Coordinator stopped during get()')


def coordinated_put(coordinator, queue, element):
    while not coordinator.should_stop():
        try:
            queue.put(element, block=True, timeout=1.0)
            return
        except Queue.Full:
            continue
    raise Exception('Coordinator stopped during put()')