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 18h => (2^16) = 65536 secs
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if self.backoff_counter < 16:
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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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