# -*- coding: utf-8 -*-
# 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 twisted.internet import defer
from synapse.appservice import ApplicationServiceState
from synapse.logging.context import run_in_background
from synapse.metrics.background_process_metrics import run_as_background_process
logger = logging.getLogger(__name__)
class ApplicationServiceScheduler(object):
""" 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()
def create_recoverer(service, callback):
return _Recoverer(self.clock, self.store, self.as_api, service, callback)
self.txn_ctrl = _TransactionController(
self.clock, self.store, self.as_api, create_recoverer
)
self.queuer = _ServiceQueuer(self.txn_ctrl, self.clock)
@defer.inlineCallbacks
def start(self):
logger.info("Starting appservice scheduler")
# check for any DOWN ASes and start recoverers for them.
recoverers = yield _Recoverer.start(
self.clock, self.store, self.as_api, self.txn_ctrl.on_recovered
)
self.txn_ctrl.add_recoverers(recoverers)
def submit_event_for_as(self, service, event):
self.queuer.enqueue(service, event)
class _ServiceQueuer(object):
"""Queues events for the same application service together, sending
transactions as soon as possible. Once a transaction is sent successfully,
this schedules any other events in the queue to run.
"""
def __init__(self, txn_ctrl, clock):
self.queued_events = {} # dict of {service_id: [events]}
self.requests_in_flight = set()
self.txn_ctrl = txn_ctrl
self.clock = clock
def enqueue(self, service, event):
self.queued_events.setdefault(service.id, []).append(event)
# 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
)
@defer.inlineCallbacks
def _send_request(self, service):
# 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:
events = self.queued_events.pop(service.id, [])
if not events:
return
try:
yield self.txn_ctrl.send(service, events)
except Exception:
logger.exception("AS request failed")
finally:
self.requests_in_flight.discard(service.id)
class _TransactionController(object):
def __init__(self, clock, store, as_api, recoverer_fn):
self.clock = clock
self.store = store
self.as_api = as_api
self.recoverer_fn = recoverer_fn
# keep track of how many recoverers there are
self.recoverers = []
@defer.inlineCallbacks
def send(self, service, events):
try:
txn = yield self.store.create_appservice_txn(service=service, events=events)
service_is_up = yield self._is_service_up(service)
if service_is_up:
sent = yield txn.send(self.as_api)
if sent:
yield txn.complete(self.store)
else:
run_in_background(self._start_recoverer, service)
except Exception:
logger.exception("Error creating appservice transaction")
run_in_background(self._start_recoverer, service)
@defer.inlineCallbacks
def on_recovered(self, recoverer):
self.recoverers.remove(recoverer)
logger.info(
"Successfully recovered application service AS ID %s", recoverer.service.id
)
logger.info("Remaining active recoverers: %s", len(self.recoverers))
yield self.store.set_appservice_state(
recoverer.service, ApplicationServiceState.UP
)
def add_recoverers(self, recoverers):
for r in recoverers:
self.recoverers.append(r)
if len(recoverers) > 0:
logger.info("New active recoverers: %s", len(self.recoverers))
@defer.inlineCallbacks
def _start_recoverer(self, service):
try:
yield self.store.set_appservice_state(service, ApplicationServiceState.DOWN)
logger.info(
"Application service falling behind. Starting recoverer. AS ID %s",
service.id,
)
recoverer = self.recoverer_fn(service, self.on_recovered)
self.add_recoverers([recoverer])
recoverer.recover()
except Exception:
logger.exception("Error starting AS recoverer")
@defer.inlineCallbacks
def _is_service_up(self, service):
state = yield self.store.get_appservice_state(service)
return state == ApplicationServiceState.UP or state is None
class _Recoverer(object):
@staticmethod
@defer.inlineCallbacks
def start(clock, store, as_api, callback):
services = yield store.get_appservices_by_state(ApplicationServiceState.DOWN)
recoverers = [_Recoverer(clock, store, as_api, s, callback) for s in services]
for r in recoverers:
logger.info(
"Starting recoverer for AS ID %s which was marked as " "DOWN",
r.service.id,
)
r.recover()
return recoverers
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()
@defer.inlineCallbacks
def retry(self):
logger.info("Starting retries on %s", self.service.id)
try:
while True:
txn = yield self.store.get_oldest_unsent_txn(self.service)
if not txn:
# nothing left: we're done!
self.callback(self)
return
logger.info(
"Retrying transaction %s for AS ID %s", txn.id, txn.service.id
)
sent = yield txn.send(self.as_api)
if not sent:
break
yield 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()