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![Kegan Dougal](/assets/img/avatar_default.png)
There's been numerous issues with people playing around with their application service and then not receiving events from their HS for ages due to backoff timers reaching crazy heights (albeit capped at < 1 day). Reduce the max time between pokes to be 8.5 minutes (2^9 secs) which is quick enough for people to wait it out (avg wait time being 4.25 min) but long enough to actually give the AS breathing room if it needs it.
255 lines
9.1 KiB
Python
255 lines
9.1 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2015 OpenMarket Ltd
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""
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This module controls the reliability for application service transactions.
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The nominal flow through this module looks like:
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__________
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1---ASa[e]-->| Service |--> Queue ASa[f]
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2----ASb[e]->| Queuer |
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3--ASa[f]--->|__________|-----------+ ASa[e], ASb[e]
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V
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-````````- +------------+
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|````````|<--StoreTxn-|Transaction |
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|Database| | Controller |---> SEND TO AS
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`--------` +------------+
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What happens on SEND TO AS depends on the state of the Application Service:
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- If the AS is marked as DOWN, do nothing.
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- If the AS is marked as UP, send the transaction.
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* SUCCESS : Increment where the AS is up to txn-wise and nuke the txn
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contents from the db.
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* FAILURE : Marked AS as DOWN and start Recoverer.
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Recoverer attempts to recover ASes who have died. The flow for this looks like:
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,--------------------- backoff++ --------------.
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V |
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START ---> Wait exp ------> Get oldest txn ID from ----> FAILURE
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backoff DB and try to send it
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^ |___________
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Mark AS as | V
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UP & quit +---------- YES SUCCESS
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| | |
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NO <--- Have more txns? <------ Mark txn success & nuke <-+
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from db; incr AS pos.
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Reset backoff.
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This is all tied together by the AppServiceScheduler which DIs the required
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components.
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"""
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from synapse.appservice import ApplicationServiceState
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from twisted.internet import defer
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import logging
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logger = logging.getLogger(__name__)
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class AppServiceScheduler(object):
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""" Public facing API for this module. Does the required DI to tie the
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components together. This also serves as the "event_pool", which in this
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case is a simple array.
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"""
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def __init__(self, clock, store, as_api):
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self.clock = clock
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self.store = store
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self.as_api = as_api
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def create_recoverer(service, callback):
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return _Recoverer(clock, store, as_api, service, callback)
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self.txn_ctrl = _TransactionController(
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clock, store, as_api, create_recoverer
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)
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self.queuer = _ServiceQueuer(self.txn_ctrl)
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@defer.inlineCallbacks
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def start(self):
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logger.info("Starting appservice scheduler")
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# check for any DOWN ASes and start recoverers for them.
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recoverers = yield _Recoverer.start(
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self.clock, self.store, self.as_api, self.txn_ctrl.on_recovered
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)
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self.txn_ctrl.add_recoverers(recoverers)
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def submit_event_for_as(self, service, event):
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self.queuer.enqueue(service, event)
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class _ServiceQueuer(object):
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"""Queues events for the same application service together, sending
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transactions as soon as possible. Once a transaction is sent successfully,
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this schedules any other events in the queue to run.
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"""
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def __init__(self, txn_ctrl):
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self.queued_events = {} # dict of {service_id: [events]}
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self.pending_requests = {} # dict of {service_id: Deferred}
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self.txn_ctrl = txn_ctrl
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def enqueue(self, service, event):
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# if this service isn't being sent something
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if not self.pending_requests.get(service.id):
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self._send_request(service, [event])
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else:
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# add to queue for this service
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if service.id not in self.queued_events:
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self.queued_events[service.id] = []
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self.queued_events[service.id].append(event)
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def _send_request(self, service, events):
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# send request and add callbacks
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d = self.txn_ctrl.send(service, events)
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d.addBoth(self._on_request_finish)
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d.addErrback(self._on_request_fail)
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self.pending_requests[service.id] = d
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def _on_request_finish(self, service):
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self.pending_requests[service.id] = None
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# if there are queued events, then send them.
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if (service.id in self.queued_events
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and len(self.queued_events[service.id]) > 0):
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self._send_request(service, self.queued_events[service.id])
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self.queued_events[service.id] = []
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def _on_request_fail(self, err):
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logger.error("AS request failed: %s", err)
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class _TransactionController(object):
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def __init__(self, clock, store, as_api, recoverer_fn):
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self.clock = clock
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self.store = store
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self.as_api = as_api
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self.recoverer_fn = recoverer_fn
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# keep track of how many recoverers there are
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self.recoverers = []
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@defer.inlineCallbacks
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def send(self, service, events):
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try:
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txn = yield self.store.create_appservice_txn(
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service=service,
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events=events
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)
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service_is_up = yield self._is_service_up(service)
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if service_is_up:
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sent = yield txn.send(self.as_api)
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if sent:
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txn.complete(self.store)
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else:
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self._start_recoverer(service)
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except Exception as e:
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logger.exception(e)
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self._start_recoverer(service)
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# request has finished
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defer.returnValue(service)
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@defer.inlineCallbacks
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def on_recovered(self, recoverer):
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self.recoverers.remove(recoverer)
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logger.info("Successfully recovered application service AS ID %s",
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recoverer.service.id)
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logger.info("Remaining active recoverers: %s", len(self.recoverers))
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yield self.store.set_appservice_state(
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recoverer.service,
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ApplicationServiceState.UP
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)
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def add_recoverers(self, recoverers):
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for r in recoverers:
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self.recoverers.append(r)
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if len(recoverers) > 0:
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logger.info("New active recoverers: %s", len(self.recoverers))
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@defer.inlineCallbacks
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def _start_recoverer(self, service):
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yield self.store.set_appservice_state(
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service,
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ApplicationServiceState.DOWN
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)
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logger.info(
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"Application service falling behind. Starting recoverer. AS ID %s",
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service.id
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)
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recoverer = self.recoverer_fn(service, self.on_recovered)
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self.add_recoverers([recoverer])
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recoverer.recover()
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@defer.inlineCallbacks
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def _is_service_up(self, service):
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state = yield self.store.get_appservice_state(service)
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defer.returnValue(state == ApplicationServiceState.UP or state is None)
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class _Recoverer(object):
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@staticmethod
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@defer.inlineCallbacks
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def start(clock, store, as_api, callback):
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services = yield store.get_appservices_by_state(
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ApplicationServiceState.DOWN
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)
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recoverers = [
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_Recoverer(clock, store, as_api, s, callback) for s in services
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]
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for r in recoverers:
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logger.info("Starting recoverer for AS ID %s which was marked as "
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"DOWN", r.service.id)
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r.recover()
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defer.returnValue(recoverers)
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def __init__(self, clock, store, as_api, service, callback):
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self.clock = clock
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self.store = store
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self.as_api = as_api
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self.service = service
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self.callback = callback
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self.backoff_counter = 1
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def recover(self):
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self.clock.call_later((2 ** self.backoff_counter), self.retry)
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def _backoff(self):
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# cap the backoff to be around 8.5min => (2^9) = 512 secs
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if self.backoff_counter < 9:
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self.backoff_counter += 1
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self.recover()
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@defer.inlineCallbacks
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def retry(self):
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try:
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txn = yield self.store.get_oldest_unsent_txn(self.service)
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if txn:
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logger.info("Retrying transaction %s for AS ID %s",
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txn.id, txn.service.id)
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sent = yield txn.send(self.as_api)
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if sent:
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yield txn.complete(self.store)
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# reset the backoff counter and retry immediately
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self.backoff_counter = 1
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yield self.retry()
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else:
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self._backoff()
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else:
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self._set_service_recovered()
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except Exception as e:
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logger.exception(e)
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self._backoff()
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def _set_service_recovered(self):
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self.callback(self)
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