OpenStack Networking (Neutron)
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# Copyright 2014 Hewlett-Packard Development Company, L.P.
# 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
# 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 datetime
from oslo_utils import timeutils
from six.moves import queue as Queue
class ResourceUpdate(object):
"""Encapsulates a resource update
An instance of this object carries the information necessary to prioritize
and process a request to update a resource.
Priority values are ordered from higher (0) to lower (>0) by the caller,
and are therefore not defined here, but must be done by the consumer.
def __init__(self, id, priority,
action=None, resource=None, timestamp=None, tries=5):
self.priority = priority
self.timestamp = timestamp
if not timestamp:
self.timestamp = timeutils.utcnow() = id
self.action = action
self.resource = resource
self.tries = tries
def __lt__(self, other):
"""Implements priority among updates
Lower numerical priority always gets precedence. When comparing two
updates of the same priority then the one with the earlier timestamp
gets precedence. In the unlikely event that the timestamps are also
equal it falls back to a simple comparison of ids meaning the
precedence is essentially random.
if self.priority != other.priority:
return self.priority < other.priority
if self.timestamp != other.timestamp:
return self.timestamp < other.timestamp
return <
def hit_retry_limit(self):
return self.tries < 0
class ExclusiveResourceProcessor(object):
"""Manager for access to a resource for processing
This class controls access to a resource in a non-blocking way. The first
instance to be created for a given ID is granted exclusive access to
the resource.
Other instances may be created for the same ID while the first
instance has exclusive access. If that happens then it doesn't block and
wait for access. Instead, it signals to the master instance that an update
came in with the timestamp.
This way, a thread will not block to wait for access to a resource.
Instead it effectively signals to the thread that is working on the
resource that something has changed since it started working on it.
That thread will simply finish its current iteration and then repeat.
This class keeps track of the last time that resource data was fetched and
processed. The timestamp that it keeps must be before when the data used
to process the resource last was fetched from the database. But, as close
as possible. The timestamp should not be recorded, however, until the
resource has been processed using the fetch data.
_masters = {}
_resource_timestamps = {}
def __init__(self, id):
self._id = id
if id not in self._masters:
self._masters[id] = self
self._queue = Queue.PriorityQueue(-1)
self._master = self._masters[id]
def _i_am_master(self):
return self == self._master
def __enter__(self):
return self
def __exit__(self, type, value, traceback):
if self._i_am_master():
del self._masters[self._id]
def _get_resource_data_timestamp(self):
return self._resource_timestamps.get(self._id,
def fetched_and_processed(self, timestamp):
"""Records the timestamp after it is used to update the resource"""
new_timestamp = max(timestamp, self._get_resource_data_timestamp())
self._resource_timestamps[self._id] = new_timestamp
def queue_update(self, update):
"""Queues an update from a worker
This is the queue used to keep new updates that come in while a
resource is being processed. These updates have already bubbled to
the front of the ResourceProcessingQueue.
def updates(self):
"""Processes the resource until updates stop coming
Only the master instance will process the resource. However, updates
may come in from other workers while it is in progress. This method
loops until they stop coming.
while self._i_am_master():
if self._queue.empty():
# Get the update from the queue even if it is old.
update = self._queue.get()
# Process the update only if it is fresh.
if self._get_resource_data_timestamp() < update.timestamp:
yield update
class ResourceProcessingQueue(object):
"""Manager of the queue of resources to process."""
def __init__(self):
self._queue = Queue.PriorityQueue()
def add(self, update):
update.tries -= 1
def each_update_to_next_resource(self):
"""Grabs the next resource from the queue and processes
This method uses a for loop to process the resource repeatedly until
updates stop bubbling to the front of the queue.
next_update = self._queue.get()
with ExclusiveResourceProcessor( as rp:
# Queue the update whether this worker is the master or not.
# Here, if the current worker is not the master, the call to
# rp.updates() will not yield and so this will essentially be a
# noop.
for update in rp.updates():
yield (rp, update)