diff --git a/synapse/federation/sender/__init__.py b/synapse/federation/sender/__init__.py
new file mode 100644
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+++ b/synapse/federation/sender/__init__.py
@@ -0,0 +1,465 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 New Vector 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.
+
+import logging
+
+from six import itervalues
+
+from prometheus_client import Counter
+
+from twisted.internet import defer
+
+import synapse.metrics
+from synapse.federation.sender.per_destination_queue import PerDestinationQueue
+from synapse.federation.sender.transaction_manager import TransactionManager
+from synapse.federation.units import Edu
+from synapse.handlers.presence import get_interested_remotes
+from synapse.metrics import (
+ LaterGauge,
+ event_processing_loop_counter,
+ event_processing_loop_room_count,
+ events_processed_counter,
+)
+from synapse.metrics.background_process_metrics import run_as_background_process
+from synapse.util import logcontext
+from synapse.util.metrics import measure_func
+
+logger = logging.getLogger(__name__)
+
+sent_pdus_destination_dist_count = Counter(
+ "synapse_federation_client_sent_pdu_destinations:count",
+ "Number of PDUs queued for sending to one or more destinations",
+)
+
+sent_pdus_destination_dist_total = Counter(
+ "synapse_federation_client_sent_pdu_destinations:total", ""
+ "Total number of PDUs queued for sending across all destinations",
+)
+
+
+class FederationSender(object):
+ def __init__(self, hs):
+ self.hs = hs
+ self.server_name = hs.hostname
+
+ self.store = hs.get_datastore()
+ self.state = hs.get_state_handler()
+
+ self.clock = hs.get_clock()
+ self.is_mine_id = hs.is_mine_id
+
+ self._transaction_manager = TransactionManager(hs)
+
+ # map from destination to PerDestinationQueue
+ self._per_destination_queues = {} # type: dict[str, PerDestinationQueue]
+
+ LaterGauge(
+ "synapse_federation_transaction_queue_pending_destinations",
+ "",
+ [],
+ lambda: sum(
+ 1 for d in self._per_destination_queues.values()
+ if d.transmission_loop_running
+ ),
+ )
+
+ # Map of user_id -> UserPresenceState for all the pending presence
+ # to be sent out by user_id. Entries here get processed and put in
+ # pending_presence_by_dest
+ self.pending_presence = {}
+
+ LaterGauge(
+ "synapse_federation_transaction_queue_pending_pdus",
+ "",
+ [],
+ lambda: sum(
+ d.pending_pdu_count() for d in self._per_destination_queues.values()
+ ),
+ )
+ LaterGauge(
+ "synapse_federation_transaction_queue_pending_edus",
+ "",
+ [],
+ lambda: sum(
+ d.pending_edu_count() for d in self._per_destination_queues.values()
+ ),
+ )
+
+ self._order = 1
+
+ self._is_processing = False
+ self._last_poked_id = -1
+
+ self._processing_pending_presence = False
+
+ # map from room_id to a set of PerDestinationQueues which we believe are
+ # awaiting a call to flush_read_receipts_for_room. The presence of an entry
+ # here for a given room means that we are rate-limiting RR flushes to that room,
+ # and that there is a pending call to _flush_rrs_for_room in the system.
+ self._queues_awaiting_rr_flush_by_room = {
+ } # type: dict[str, set[PerDestinationQueue]]
+
+ self._rr_txn_interval_per_room_ms = (
+ 1000.0 / hs.get_config().federation_rr_transactions_per_room_per_second
+ )
+
+ def _get_per_destination_queue(self, destination):
+ """Get or create a PerDestinationQueue for the given destination
+
+ Args:
+ destination (str): server_name of remote server
+
+ Returns:
+ PerDestinationQueue
+ """
+ queue = self._per_destination_queues.get(destination)
+ if not queue:
+ queue = PerDestinationQueue(self.hs, self._transaction_manager, destination)
+ self._per_destination_queues[destination] = queue
+ return queue
+
+ def notify_new_events(self, current_id):
+ """This gets called when we have some new events we might want to
+ send out to other servers.
+ """
+ self._last_poked_id = max(current_id, self._last_poked_id)
+
+ if self._is_processing:
+ return
+
+ # fire off a processing loop in the background
+ run_as_background_process(
+ "process_event_queue_for_federation",
+ self._process_event_queue_loop,
+ )
+
+ @defer.inlineCallbacks
+ def _process_event_queue_loop(self):
+ try:
+ self._is_processing = True
+ while True:
+ last_token = yield self.store.get_federation_out_pos("events")
+ next_token, events = yield self.store.get_all_new_events_stream(
+ last_token, self._last_poked_id, limit=100,
+ )
+
+ logger.debug("Handling %s -> %s", last_token, next_token)
+
+ if not events and next_token >= self._last_poked_id:
+ break
+
+ @defer.inlineCallbacks
+ def handle_event(event):
+ # Only send events for this server.
+ send_on_behalf_of = event.internal_metadata.get_send_on_behalf_of()
+ is_mine = self.is_mine_id(event.sender)
+ if not is_mine and send_on_behalf_of is None:
+ return
+
+ try:
+ # Get the state from before the event.
+ # We need to make sure that this is the state from before
+ # the event and not from after it.
+ # Otherwise if the last member on a server in a room is
+ # banned then it won't receive the event because it won't
+ # be in the room after the ban.
+ destinations = yield self.state.get_current_hosts_in_room(
+ event.room_id, latest_event_ids=event.prev_event_ids(),
+ )
+ except Exception:
+ logger.exception(
+ "Failed to calculate hosts in room for event: %s",
+ event.event_id,
+ )
+ return
+
+ destinations = set(destinations)
+
+ if send_on_behalf_of is not None:
+ # If we are sending the event on behalf of another server
+ # then it already has the event and there is no reason to
+ # send the event to it.
+ destinations.discard(send_on_behalf_of)
+
+ logger.debug("Sending %s to %r", event, destinations)
+
+ self._send_pdu(event, destinations)
+
+ @defer.inlineCallbacks
+ def handle_room_events(events):
+ for event in events:
+ yield handle_event(event)
+
+ events_by_room = {}
+ for event in events:
+ events_by_room.setdefault(event.room_id, []).append(event)
+
+ yield logcontext.make_deferred_yieldable(defer.gatherResults(
+ [
+ logcontext.run_in_background(handle_room_events, evs)
+ for evs in itervalues(events_by_room)
+ ],
+ consumeErrors=True
+ ))
+
+ yield self.store.update_federation_out_pos(
+ "events", next_token
+ )
+
+ if events:
+ now = self.clock.time_msec()
+ ts = yield self.store.get_received_ts(events[-1].event_id)
+
+ synapse.metrics.event_processing_lag.labels(
+ "federation_sender").set(now - ts)
+ synapse.metrics.event_processing_last_ts.labels(
+ "federation_sender").set(ts)
+
+ events_processed_counter.inc(len(events))
+
+ event_processing_loop_room_count.labels(
+ "federation_sender"
+ ).inc(len(events_by_room))
+
+ event_processing_loop_counter.labels("federation_sender").inc()
+
+ synapse.metrics.event_processing_positions.labels(
+ "federation_sender").set(next_token)
+
+ finally:
+ self._is_processing = False
+
+ def _send_pdu(self, pdu, destinations):
+ # We loop through all destinations to see whether we already have
+ # a transaction in progress. If we do, stick it in the pending_pdus
+ # table and we'll get back to it later.
+
+ order = self._order
+ self._order += 1
+
+ destinations = set(destinations)
+ destinations.discard(self.server_name)
+ logger.debug("Sending to: %s", str(destinations))
+
+ if not destinations:
+ return
+
+ sent_pdus_destination_dist_total.inc(len(destinations))
+ sent_pdus_destination_dist_count.inc()
+
+ for destination in destinations:
+ self._get_per_destination_queue(destination).send_pdu(pdu, order)
+
+ @defer.inlineCallbacks
+ def send_read_receipt(self, receipt):
+ """Send a RR to any other servers in the room
+
+ Args:
+ receipt (synapse.types.ReadReceipt): receipt to be sent
+ """
+
+ # Some background on the rate-limiting going on here.
+ #
+ # It turns out that if we attempt to send out RRs as soon as we get them from
+ # a client, then we end up trying to do several hundred Hz of federation
+ # transactions. (The number of transactions scales as O(N^2) on the size of a
+ # room, since in a large room we have both more RRs coming in, and more servers
+ # to send them to.)
+ #
+ # This leads to a lot of CPU load, and we end up getting behind. The solution
+ # currently adopted is as follows:
+ #
+ # The first receipt in a given room is sent out immediately, at time T0. Any
+ # further receipts are, in theory, batched up for N seconds, where N is calculated
+ # based on the number of servers in the room to achieve a transaction frequency
+ # of around 50Hz. So, for example, if there were 100 servers in the room, then
+ # N would be 100 / 50Hz = 2 seconds.
+ #
+ # Then, after T+N, we flush out any receipts that have accumulated, and restart
+ # the timer to flush out more receipts at T+2N, etc. If no receipts accumulate,
+ # we stop the cycle and go back to the start.
+ #
+ # However, in practice, it is often possible to flush out receipts earlier: in
+ # particular, if we are sending a transaction to a given server anyway (for
+ # example, because we have a PDU or a RR in another room to send), then we may
+ # as well send out all of the pending RRs for that server. So it may be that
+ # by the time we get to T+N, we don't actually have any RRs left to send out.
+ # Nevertheless we continue to buffer up RRs for the room in question until we
+ # reach the point that no RRs arrive between timer ticks.
+ #
+ # For even more background, see https://github.com/matrix-org/synapse/issues/4730.
+
+ room_id = receipt.room_id
+
+ # Work out which remote servers should be poked and poke them.
+ domains = yield self.state.get_current_hosts_in_room(room_id)
+ domains = [d for d in domains if d != self.server_name]
+ if not domains:
+ return
+
+ queues_pending_flush = self._queues_awaiting_rr_flush_by_room.get(
+ room_id
+ )
+
+ # if there is no flush yet scheduled, we will send out these receipts with
+ # immediate flushes, and schedule the next flush for this room.
+ if queues_pending_flush is not None:
+ logger.debug("Queuing receipt for: %r", domains)
+ else:
+ logger.debug("Sending receipt to: %r", domains)
+ self._schedule_rr_flush_for_room(room_id, len(domains))
+
+ for domain in domains:
+ queue = self._get_per_destination_queue(domain)
+ queue.queue_read_receipt(receipt)
+
+ # if there is already a RR flush pending for this room, then make sure this
+ # destination is registered for the flush
+ if queues_pending_flush is not None:
+ queues_pending_flush.add(queue)
+ else:
+ queue.flush_read_receipts_for_room(room_id)
+
+ def _schedule_rr_flush_for_room(self, room_id, n_domains):
+ # that is going to cause approximately len(domains) transactions, so now back
+ # off for that multiplied by RR_TXN_INTERVAL_PER_ROOM
+ backoff_ms = self._rr_txn_interval_per_room_ms * n_domains
+
+ logger.debug("Scheduling RR flush in %s in %d ms", room_id, backoff_ms)
+ self.clock.call_later(backoff_ms, self._flush_rrs_for_room, room_id)
+ self._queues_awaiting_rr_flush_by_room[room_id] = set()
+
+ def _flush_rrs_for_room(self, room_id):
+ queues = self._queues_awaiting_rr_flush_by_room.pop(room_id)
+ logger.debug("Flushing RRs in %s to %s", room_id, queues)
+
+ if not queues:
+ # no more RRs arrived for this room; we are done.
+ return
+
+ # schedule the next flush
+ self._schedule_rr_flush_for_room(room_id, len(queues))
+
+ for queue in queues:
+ queue.flush_read_receipts_for_room(room_id)
+
+ @logcontext.preserve_fn # the caller should not yield on this
+ @defer.inlineCallbacks
+ def send_presence(self, states):
+ """Send the new presence states to the appropriate destinations.
+
+ This actually queues up the presence states ready for sending and
+ triggers a background task to process them and send out the transactions.
+
+ Args:
+ states (list(UserPresenceState))
+ """
+ if not self.hs.config.use_presence:
+ # No-op if presence is disabled.
+ return
+
+ # First we queue up the new presence by user ID, so multiple presence
+ # updates in quick successtion are correctly handled
+ # We only want to send presence for our own users, so lets always just
+ # filter here just in case.
+ self.pending_presence.update({
+ state.user_id: state for state in states
+ if self.is_mine_id(state.user_id)
+ })
+
+ # We then handle the new pending presence in batches, first figuring
+ # out the destinations we need to send each state to and then poking it
+ # to attempt a new transaction. We linearize this so that we don't
+ # accidentally mess up the ordering and send multiple presence updates
+ # in the wrong order
+ if self._processing_pending_presence:
+ return
+
+ self._processing_pending_presence = True
+ try:
+ while True:
+ states_map = self.pending_presence
+ self.pending_presence = {}
+
+ if not states_map:
+ break
+
+ yield self._process_presence_inner(list(states_map.values()))
+ except Exception:
+ logger.exception("Error sending presence states to servers")
+ finally:
+ self._processing_pending_presence = False
+
+ @measure_func("txnqueue._process_presence")
+ @defer.inlineCallbacks
+ def _process_presence_inner(self, states):
+ """Given a list of states populate self.pending_presence_by_dest and
+ poke to send a new transaction to each destination
+
+ Args:
+ states (list(UserPresenceState))
+ """
+ hosts_and_states = yield get_interested_remotes(self.store, states, self.state)
+
+ for destinations, states in hosts_and_states:
+ for destination in destinations:
+ if destination == self.server_name:
+ continue
+ self._get_per_destination_queue(destination).send_presence(states)
+
+ def build_and_send_edu(self, destination, edu_type, content, key=None):
+ """Construct an Edu object, and queue it for sending
+
+ Args:
+ destination (str): name of server to send to
+ edu_type (str): type of EDU to send
+ content (dict): content of EDU
+ key (Any|None): clobbering key for this edu
+ """
+ if destination == self.server_name:
+ logger.info("Not sending EDU to ourselves")
+ return
+
+ edu = Edu(
+ origin=self.server_name,
+ destination=destination,
+ edu_type=edu_type,
+ content=content,
+ )
+
+ self.send_edu(edu, key)
+
+ def send_edu(self, edu, key):
+ """Queue an EDU for sending
+
+ Args:
+ edu (Edu): edu to send
+ key (Any|None): clobbering key for this edu
+ """
+ queue = self._get_per_destination_queue(edu.destination)
+ if key:
+ queue.send_keyed_edu(edu, key)
+ else:
+ queue.send_edu(edu)
+
+ def send_device_messages(self, destination):
+ if destination == self.server_name:
+ logger.info("Not sending device update to ourselves")
+ return
+
+ self._get_per_destination_queue(destination).attempt_new_transaction()
+
+ def get_current_token(self):
+ return 0
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