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- # Copyright 2015, 2016 OpenMarket Ltd
- #
- # 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.
- """
- This module controls the reliability for application service transactions.
-
- The nominal flow through this module looks like:
- __________
- 1---ASa[e]-->| Service |--> Queue ASa[f]
- 2----ASb[e]->| Queuer |
- 3--ASa[f]--->|__________|-----------+ ASa[e], ASb[e]
- V
- -````````- +------------+
- |````````|<--StoreTxn-|Transaction |
- |Database| | Controller |---> SEND TO AS
- `--------` +------------+
- What happens on SEND TO AS depends on the state of the Application Service:
- - If the AS is marked as DOWN, do nothing.
- - If the AS is marked as UP, send the transaction.
- * SUCCESS : Increment where the AS is up to txn-wise and nuke the txn
- contents from the db.
- * FAILURE : Marked AS as DOWN and start Recoverer.
-
- Recoverer attempts to recover ASes who have died. The flow for this looks like:
- ,--------------------- backoff++ --------------.
- V |
- START ---> Wait exp ------> Get oldest txn ID from ----> FAILURE
- backoff DB and try to send it
- ^ |___________
- Mark AS as | V
- UP & quit +---------- YES SUCCESS
- | | |
- NO <--- Have more txns? <------ Mark txn success & nuke <-+
- from db; incr AS pos.
- Reset backoff.
-
- This is all tied together by the AppServiceScheduler which DIs the required
- components.
- """
- import logging
- from typing import List, Optional
-
- from synapse.appservice import ApplicationService, ApplicationServiceState
- from synapse.events import EventBase
- from synapse.logging.context import run_in_background
- from synapse.metrics.background_process_metrics import run_as_background_process
- from synapse.types import JsonDict
-
- logger = logging.getLogger(__name__)
-
-
- # Maximum number of events to provide in an AS transaction.
- MAX_PERSISTENT_EVENTS_PER_TRANSACTION = 100
-
- # Maximum number of ephemeral events to provide in an AS transaction.
- MAX_EPHEMERAL_EVENTS_PER_TRANSACTION = 100
-
-
- class ApplicationServiceScheduler:
- """Public facing API for this module. Does the required DI to tie the
- components together. This also serves as the "event_pool", which in this
- case is a simple array.
- """
-
- def __init__(self, hs):
- self.clock = hs.get_clock()
- self.store = hs.get_datastore()
- self.as_api = hs.get_application_service_api()
-
- self.txn_ctrl = _TransactionController(self.clock, self.store, self.as_api)
- self.queuer = _ServiceQueuer(self.txn_ctrl, self.clock)
-
- async def start(self):
- logger.info("Starting appservice scheduler")
-
- # check for any DOWN ASes and start recoverers for them.
- services = await self.store.get_appservices_by_state(
- ApplicationServiceState.DOWN
- )
-
- for service in services:
- self.txn_ctrl.start_recoverer(service)
-
- def submit_event_for_as(self, service: ApplicationService, event: EventBase):
- self.queuer.enqueue_event(service, event)
-
- def submit_ephemeral_events_for_as(
- self, service: ApplicationService, events: List[JsonDict]
- ):
- self.queuer.enqueue_ephemeral(service, events)
-
-
- class _ServiceQueuer:
- """Queue of events waiting to be sent to appservices.
-
- Groups events into transactions per-appservice, and sends them on to the
- TransactionController. Makes sure that we only have one transaction in flight per
- appservice at a given time.
- """
-
- def __init__(self, txn_ctrl, clock):
- self.queued_events = {} # dict of {service_id: [events]}
- self.queued_ephemeral = {} # dict of {service_id: [events]}
-
- # the appservices which currently have a transaction in flight
- self.requests_in_flight = set()
- self.txn_ctrl = txn_ctrl
- self.clock = clock
-
- def _start_background_request(self, service):
- # start a sender for this appservice if we don't already have one
- if service.id in self.requests_in_flight:
- return
-
- run_as_background_process(
- "as-sender-%s" % (service.id,), self._send_request, service
- )
-
- def enqueue_event(self, service: ApplicationService, event: EventBase):
- self.queued_events.setdefault(service.id, []).append(event)
- self._start_background_request(service)
-
- def enqueue_ephemeral(self, service: ApplicationService, events: List[JsonDict]):
- self.queued_ephemeral.setdefault(service.id, []).extend(events)
- self._start_background_request(service)
-
- async def _send_request(self, service: ApplicationService):
- # sanity-check: we shouldn't get here if this service already has a sender
- # running.
- assert service.id not in self.requests_in_flight
-
- self.requests_in_flight.add(service.id)
- try:
- while True:
- all_events = self.queued_events.get(service.id, [])
- events = all_events[:MAX_PERSISTENT_EVENTS_PER_TRANSACTION]
- del all_events[:MAX_PERSISTENT_EVENTS_PER_TRANSACTION]
-
- all_events_ephemeral = self.queued_ephemeral.get(service.id, [])
- ephemeral = all_events_ephemeral[:MAX_EPHEMERAL_EVENTS_PER_TRANSACTION]
- del all_events_ephemeral[:MAX_EPHEMERAL_EVENTS_PER_TRANSACTION]
-
- if not events and not ephemeral:
- return
-
- try:
- await self.txn_ctrl.send(service, events, ephemeral)
- except Exception:
- logger.exception("AS request failed")
- finally:
- self.requests_in_flight.discard(service.id)
-
-
- class _TransactionController:
- """Transaction manager.
-
- Builds AppServiceTransactions and runs their lifecycle. Also starts a Recoverer
- if a transaction fails.
-
- (Note we have only have one of these in the homeserver.)
-
- Args:
- clock (synapse.util.Clock):
- store (synapse.storage.DataStore):
- as_api (synapse.appservice.api.ApplicationServiceApi):
- """
-
- def __init__(self, clock, store, as_api):
- self.clock = clock
- self.store = store
- self.as_api = as_api
-
- # map from service id to recoverer instance
- self.recoverers = {}
-
- # for UTs
- self.RECOVERER_CLASS = _Recoverer
-
- async def send(
- self,
- service: ApplicationService,
- events: List[EventBase],
- ephemeral: Optional[List[JsonDict]] = None,
- ):
- try:
- txn = await self.store.create_appservice_txn(
- service=service, events=events, ephemeral=ephemeral or []
- )
- service_is_up = await self._is_service_up(service)
- if service_is_up:
- sent = await txn.send(self.as_api)
- if sent:
- await txn.complete(self.store)
- else:
- run_in_background(self._on_txn_fail, service)
- except Exception:
- logger.exception("Error creating appservice transaction")
- run_in_background(self._on_txn_fail, service)
-
- async def on_recovered(self, recoverer):
- logger.info(
- "Successfully recovered application service AS ID %s", recoverer.service.id
- )
- self.recoverers.pop(recoverer.service.id)
- logger.info("Remaining active recoverers: %s", len(self.recoverers))
- await self.store.set_appservice_state(
- recoverer.service, ApplicationServiceState.UP
- )
-
- async def _on_txn_fail(self, service):
- try:
- await self.store.set_appservice_state(service, ApplicationServiceState.DOWN)
- self.start_recoverer(service)
- except Exception:
- logger.exception("Error starting AS recoverer")
-
- def start_recoverer(self, service):
- """Start a Recoverer for the given service
-
- Args:
- service (synapse.appservice.ApplicationService):
- """
- logger.info("Starting recoverer for AS ID %s", service.id)
- assert service.id not in self.recoverers
- recoverer = self.RECOVERER_CLASS(
- self.clock, self.store, self.as_api, service, self.on_recovered
- )
- self.recoverers[service.id] = recoverer
- recoverer.recover()
- logger.info("Now %i active recoverers", len(self.recoverers))
-
- async def _is_service_up(self, service: ApplicationService) -> bool:
- state = await self.store.get_appservice_state(service)
- return state == ApplicationServiceState.UP or state is None
-
-
- class _Recoverer:
- """Manages retries and backoff for a DOWN appservice.
-
- We have one of these for each appservice which is currently considered DOWN.
-
- Args:
- clock (synapse.util.Clock):
- store (synapse.storage.DataStore):
- as_api (synapse.appservice.api.ApplicationServiceApi):
- service (synapse.appservice.ApplicationService): the service we are managing
- callback (callable[_Recoverer]): called once the service recovers.
- """
-
- def __init__(self, clock, store, as_api, service, callback):
- self.clock = clock
- self.store = store
- self.as_api = as_api
- self.service = service
- self.callback = callback
- self.backoff_counter = 1
-
- def recover(self):
- def _retry():
- run_as_background_process(
- "as-recoverer-%s" % (self.service.id,), self.retry
- )
-
- delay = 2 ** self.backoff_counter
- logger.info("Scheduling retries on %s in %fs", self.service.id, delay)
- self.clock.call_later(delay, _retry)
-
- def _backoff(self):
- # cap the backoff to be around 8.5min => (2^9) = 512 secs
- if self.backoff_counter < 9:
- self.backoff_counter += 1
- self.recover()
-
- async def retry(self):
- logger.info("Starting retries on %s", self.service.id)
- try:
- while True:
- txn = await self.store.get_oldest_unsent_txn(self.service)
- if not txn:
- # nothing left: we're done!
- await self.callback(self)
- return
-
- logger.info(
- "Retrying transaction %s for AS ID %s", txn.id, txn.service.id
- )
- sent = await txn.send(self.as_api)
- if not sent:
- break
-
- await txn.complete(self.store)
-
- # reset the backoff counter and then process the next transaction
- self.backoff_counter = 1
-
- except Exception:
- logger.exception("Unexpected error running retries")
-
- # we didn't manage to send all of the transactions before we got an error of
- # some flavour: reschedule the next retry.
- self._backoff()
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