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-rw-r--r--synapse/handlers/presence.py364
1 files changed, 267 insertions, 97 deletions
diff --git a/synapse/handlers/presence.py b/synapse/handlers/presence.py
index d0c8f1328b..1b89dc6274 100644
--- a/synapse/handlers/presence.py
+++ b/synapse/handlers/presence.py
@@ -33,11 +33,9 @@ from synapse.util.logcontext import preserve_fn
 from synapse.util.logutils import log_function
 from synapse.util.metrics import Measure
 from synapse.util.wheel_timer import WheelTimer
-from synapse.types import UserID
+from synapse.types import UserID, get_domain_from_id
 import synapse.metrics
 
-from ._base import BaseHandler
-
 import logging
 
 
@@ -52,6 +50,13 @@ timers_fired_counter = metrics.register_counter("timers_fired")
 federation_presence_counter = metrics.register_counter("federation_presence")
 bump_active_time_counter = metrics.register_counter("bump_active_time")
 
+get_updates_counter = metrics.register_counter("get_updates", labels=["type"])
+
+notify_reason_counter = metrics.register_counter("notify_reason", labels=["reason"])
+state_transition_counter = metrics.register_counter(
+    "state_transition", labels=["from", "to"]
+)
+
 
 # If a user was last active in the last LAST_ACTIVE_GRANULARITY, consider them
 # "currently_active"
@@ -70,38 +75,45 @@ FEDERATION_TIMEOUT = 30 * 60 * 1000
 # How often to resend presence to remote servers
 FEDERATION_PING_INTERVAL = 25 * 60 * 1000
 
+# How long we will wait before assuming that the syncs from an external process
+# are dead.
+EXTERNAL_PROCESS_EXPIRY = 5 * 60 * 1000
+
 assert LAST_ACTIVE_GRANULARITY < IDLE_TIMER
 
 
-class PresenceHandler(BaseHandler):
+class PresenceHandler(object):
 
     def __init__(self, hs):
-        super(PresenceHandler, self).__init__(hs)
-        self.hs = hs
+        self.is_mine = hs.is_mine
+        self.is_mine_id = hs.is_mine_id
         self.clock = hs.get_clock()
         self.store = hs.get_datastore()
         self.wheel_timer = WheelTimer()
         self.notifier = hs.get_notifier()
-        self.federation = hs.get_replication_layer()
+        self.replication = hs.get_replication_layer()
+        self.federation = hs.get_federation_sender()
+
+        self.state = hs.get_state_handler()
 
-        self.federation.register_edu_handler(
+        self.replication.register_edu_handler(
             "m.presence", self.incoming_presence
         )
-        self.federation.register_edu_handler(
+        self.replication.register_edu_handler(
             "m.presence_invite",
             lambda origin, content: self.invite_presence(
                 observed_user=UserID.from_string(content["observed_user"]),
                 observer_user=UserID.from_string(content["observer_user"]),
             )
         )
-        self.federation.register_edu_handler(
+        self.replication.register_edu_handler(
             "m.presence_accept",
             lambda origin, content: self.accept_presence(
                 observed_user=UserID.from_string(content["observed_user"]),
                 observer_user=UserID.from_string(content["observer_user"]),
             )
         )
-        self.federation.register_edu_handler(
+        self.replication.register_edu_handler(
             "m.presence_deny",
             lambda origin, content: self.deny_presence(
                 observed_user=UserID.from_string(content["observed_user"]),
@@ -138,7 +150,7 @@ class PresenceHandler(BaseHandler):
                 obj=state.user_id,
                 then=state.last_user_sync_ts + SYNC_ONLINE_TIMEOUT,
             )
-            if self.hs.is_mine_id(state.user_id):
+            if self.is_mine_id(state.user_id):
                 self.wheel_timer.insert(
                     now=now,
                     obj=state.user_id,
@@ -160,20 +172,38 @@ class PresenceHandler(BaseHandler):
         self.serial_to_user = {}
         self._next_serial = 1
 
-        # Keeps track of the number of *ongoing* syncs. While this is non zero
-        # a user will never go offline.
+        # Keeps track of the number of *ongoing* syncs on this process. While
+        # this is non zero a user will never go offline.
         self.user_to_num_current_syncs = {}
 
+        # Keeps track of the number of *ongoing* syncs on other processes.
+        # While any sync is ongoing on another process the user will never
+        # go offline.
+        # Each process has a unique identifier and an update frequency. If
+        # no update is received from that process within the update period then
+        # we assume that all the sync requests on that process have stopped.
+        # Stored as a dict from process_id to set of user_id, and a dict of
+        # process_id to millisecond timestamp last updated.
+        self.external_process_to_current_syncs = {}
+        self.external_process_last_updated_ms = {}
+
         # Start a LoopingCall in 30s that fires every 5s.
         # The initial delay is to allow disconnected clients a chance to
         # reconnect before we treat them as offline.
         self.clock.call_later(
-            0 * 1000,
+            30,
             self.clock.looping_call,
             self._handle_timeouts,
             5000,
         )
 
+        self.clock.call_later(
+            60,
+            self.clock.looping_call,
+            self._persist_unpersisted_changes,
+            60 * 1000,
+        )
+
         metrics.register_callback("wheel_timer_size", lambda: len(self.wheel_timer))
 
     @defer.inlineCallbacks
@@ -188,7 +218,7 @@ class PresenceHandler(BaseHandler):
         is some spurious presence changes that will self-correct.
         """
         logger.info(
-            "Performing _on_shutdown. Persiting %d unpersisted changes",
+            "Performing _on_shutdown. Persisting %d unpersisted changes",
             len(self.user_to_current_state)
         )
 
@@ -200,6 +230,27 @@ class PresenceHandler(BaseHandler):
         logger.info("Finished _on_shutdown")
 
     @defer.inlineCallbacks
+    def _persist_unpersisted_changes(self):
+        """We periodically persist the unpersisted changes, as otherwise they
+        may stack up and slow down shutdown times.
+        """
+        logger.info(
+            "Performing _persist_unpersisted_changes. Persisting %d unpersisted changes",
+            len(self.unpersisted_users_changes)
+        )
+
+        unpersisted = self.unpersisted_users_changes
+        self.unpersisted_users_changes = set()
+
+        if unpersisted:
+            yield self.store.update_presence([
+                self.user_to_current_state[user_id]
+                for user_id in unpersisted
+            ])
+
+        logger.info("Finished _persist_unpersisted_changes")
+
+    @defer.inlineCallbacks
     def _update_states(self, new_states):
         """Updates presence of users. Sets the appropriate timeouts. Pokes
         the notifier and federation if and only if the changed presence state
@@ -215,6 +266,12 @@ class PresenceHandler(BaseHandler):
             to_notify = {}  # Changes we want to notify everyone about
             to_federation_ping = {}  # These need sending keep-alives
 
+            # Only bother handling the last presence change for each user
+            new_states_dict = {}
+            for new_state in new_states:
+                new_states_dict[new_state.user_id] = new_state
+            new_state = new_states_dict.values()
+
             for new_state in new_states:
                 user_id = new_state.user_id
 
@@ -228,7 +285,7 @@ class PresenceHandler(BaseHandler):
 
                 new_state, should_notify, should_ping = handle_update(
                     prev_state, new_state,
-                    is_mine=self.hs.is_mine_id(user_id),
+                    is_mine=self.is_mine_id(user_id),
                     wheel_timer=self.wheel_timer,
                     now=now
                 )
@@ -268,31 +325,48 @@ class PresenceHandler(BaseHandler):
         """Checks the presence of users that have timed out and updates as
         appropriate.
         """
+        logger.info("Handling presence timeouts")
         now = self.clock.time_msec()
 
-        with Measure(self.clock, "presence_handle_timeouts"):
-            # Fetch the list of users that *may* have timed out. Things may have
-            # changed since the timeout was set, so we won't necessarily have to
-            # take any action.
-            users_to_check = self.wheel_timer.fetch(now)
+        try:
+            with Measure(self.clock, "presence_handle_timeouts"):
+                # Fetch the list of users that *may* have timed out. Things may have
+                # changed since the timeout was set, so we won't necessarily have to
+                # take any action.
+                users_to_check = set(self.wheel_timer.fetch(now))
+
+                # Check whether the lists of syncing processes from an external
+                # process have expired.
+                expired_process_ids = [
+                    process_id for process_id, last_update
+                    in self.external_process_last_updated_ms.items()
+                    if now - last_update > EXTERNAL_PROCESS_EXPIRY
+                ]
+                for process_id in expired_process_ids:
+                    users_to_check.update(
+                        self.external_process_last_updated_ms.pop(process_id, ())
+                    )
+                    self.external_process_last_update.pop(process_id)
 
-            states = [
-                self.user_to_current_state.get(
-                    user_id, UserPresenceState.default(user_id)
-                )
-                for user_id in set(users_to_check)
-            ]
+                states = [
+                    self.user_to_current_state.get(
+                        user_id, UserPresenceState.default(user_id)
+                    )
+                    for user_id in users_to_check
+                ]
 
-            timers_fired_counter.inc_by(len(states))
+                timers_fired_counter.inc_by(len(states))
 
-            changes = handle_timeouts(
-                states,
-                is_mine_fn=self.hs.is_mine_id,
-                user_to_num_current_syncs=self.user_to_num_current_syncs,
-                now=now,
-            )
+                changes = handle_timeouts(
+                    states,
+                    is_mine_fn=self.is_mine_id,
+                    syncing_user_ids=self.get_currently_syncing_users(),
+                    now=now,
+                )
 
-        preserve_fn(self._update_states)(changes)
+            preserve_fn(self._update_states)(changes)
+        except:
+            logger.exception("Exception in _handle_timeouts loop")
 
     @defer.inlineCallbacks
     def bump_presence_active_time(self, user):
@@ -365,6 +439,74 @@ class PresenceHandler(BaseHandler):
 
         defer.returnValue(_user_syncing())
 
+    def get_currently_syncing_users(self):
+        """Get the set of user ids that are currently syncing on this HS.
+        Returns:
+            set(str): A set of user_id strings.
+        """
+        syncing_user_ids = {
+            user_id for user_id, count in self.user_to_num_current_syncs.items()
+            if count
+        }
+        for user_ids in self.external_process_to_current_syncs.values():
+            syncing_user_ids.update(user_ids)
+        return syncing_user_ids
+
+    @defer.inlineCallbacks
+    def update_external_syncs(self, process_id, syncing_user_ids):
+        """Update the syncing users for an external process
+
+        Args:
+            process_id(str): An identifier for the process the users are
+                syncing against. This allows synapse to process updates
+                as user start and stop syncing against a given process.
+            syncing_user_ids(set(str)): The set of user_ids that are
+                currently syncing on that server.
+        """
+
+        # Grab the previous list of user_ids that were syncing on that process
+        prev_syncing_user_ids = (
+            self.external_process_to_current_syncs.get(process_id, set())
+        )
+        # Grab the current presence state for both the users that are syncing
+        # now and the users that were syncing before this update.
+        prev_states = yield self.current_state_for_users(
+            syncing_user_ids | prev_syncing_user_ids
+        )
+        updates = []
+        time_now_ms = self.clock.time_msec()
+
+        # For each new user that is syncing check if we need to mark them as
+        # being online.
+        for new_user_id in syncing_user_ids - prev_syncing_user_ids:
+            prev_state = prev_states[new_user_id]
+            if prev_state.state == PresenceState.OFFLINE:
+                updates.append(prev_state.copy_and_replace(
+                    state=PresenceState.ONLINE,
+                    last_active_ts=time_now_ms,
+                    last_user_sync_ts=time_now_ms,
+                ))
+            else:
+                updates.append(prev_state.copy_and_replace(
+                    last_user_sync_ts=time_now_ms,
+                ))
+
+        # For each user that is still syncing or stopped syncing update the
+        # last sync time so that we will correctly apply the grace period when
+        # they stop syncing.
+        for old_user_id in prev_syncing_user_ids:
+            prev_state = prev_states[old_user_id]
+            updates.append(prev_state.copy_and_replace(
+                last_user_sync_ts=time_now_ms,
+            ))
+
+        yield self._update_states(updates)
+
+        # Update the last updated time for the process. We expire the entries
+        # if we don't receive an update in the given timeframe.
+        self.external_process_last_updated_ms[process_id] = self.clock.time_msec()
+        self.external_process_to_current_syncs[process_id] = syncing_user_ids
+
     @defer.inlineCallbacks
     def current_state_for_user(self, user_id):
         """Get the current presence state for a user.
@@ -403,7 +545,7 @@ class PresenceHandler(BaseHandler):
         defer.returnValue(states)
 
     @defer.inlineCallbacks
-    def _get_interested_parties(self, states):
+    def _get_interested_parties(self, states, calculate_remote_hosts=True):
         """Given a list of states return which entities (rooms, users, servers)
         are interested in the given states.
 
@@ -426,21 +568,24 @@ class PresenceHandler(BaseHandler):
             users_to_states.setdefault(state.user_id, []).append(state)
 
         hosts_to_states = {}
-        for room_id, states in room_ids_to_states.items():
-            local_states = filter(lambda s: self.hs.is_mine_id(s.user_id), states)
-            if not local_states:
-                continue
+        if calculate_remote_hosts:
+            for room_id, states in room_ids_to_states.items():
+                local_states = filter(lambda s: self.is_mine_id(s.user_id), states)
+                if not local_states:
+                    continue
+
+                users = yield self.state.get_current_user_in_room(room_id)
+                hosts = set(get_domain_from_id(u) for u in users)
 
-            hosts = yield self.store.get_joined_hosts_for_room(room_id)
-            for host in hosts:
-                hosts_to_states.setdefault(host, []).extend(local_states)
+                for host in hosts:
+                    hosts_to_states.setdefault(host, []).extend(local_states)
 
         for user_id, states in users_to_states.items():
-            local_states = filter(lambda s: self.hs.is_mine_id(s.user_id), states)
+            local_states = filter(lambda s: self.is_mine_id(s.user_id), states)
             if not local_states:
                 continue
 
-            host = UserID.from_string(user_id).domain
+            host = get_domain_from_id(user_id)
             hosts_to_states.setdefault(host, []).extend(local_states)
 
         # TODO: de-dup hosts_to_states, as a single host might have multiple
@@ -465,24 +610,24 @@ class PresenceHandler(BaseHandler):
 
         self._push_to_remotes(hosts_to_states)
 
+    @defer.inlineCallbacks
+    def notify_for_states(self, state, stream_id):
+        parties = yield self._get_interested_parties([state])
+        room_ids_to_states, users_to_states, hosts_to_states = parties
+
+        self.notifier.on_new_event(
+            "presence_key", stream_id, rooms=room_ids_to_states.keys(),
+            users=[UserID.from_string(u) for u in users_to_states.keys()]
+        )
+
     def _push_to_remotes(self, hosts_to_states):
         """Sends state updates to remote servers.
 
         Args:
             hosts_to_states (dict): Mapping `server_name` -> `[UserPresenceState]`
         """
-        now = self.clock.time_msec()
         for host, states in hosts_to_states.items():
-            self.federation.send_edu(
-                destination=host,
-                edu_type="m.presence",
-                content={
-                    "push": [
-                        _format_user_presence_state(state, now)
-                        for state in states
-                    ]
-                }
-            )
+            self.federation.send_presence(host, states)
 
     @defer.inlineCallbacks
     def incoming_presence(self, origin, content):
@@ -503,6 +648,13 @@ class PresenceHandler(BaseHandler):
                 )
                 continue
 
+            if get_domain_from_id(user_id) != origin:
+                logger.info(
+                    "Got presence update from %r with bad 'user_id': %r",
+                    origin, user_id,
+                )
+                continue
+
             presence_state = push.get("presence", None)
             if not presence_state:
                 logger.info(
@@ -562,17 +714,17 @@ class PresenceHandler(BaseHandler):
             defer.returnValue([
                 {
                     "type": "m.presence",
-                    "content": _format_user_presence_state(state, now),
+                    "content": format_user_presence_state(state, now),
                 }
                 for state in updates
             ])
         else:
             defer.returnValue([
-                _format_user_presence_state(state, now) for state in updates
+                format_user_presence_state(state, now) for state in updates
             ])
 
     @defer.inlineCallbacks
-    def set_state(self, target_user, state):
+    def set_state(self, target_user, state, ignore_status_msg=False):
         """Set the presence state of the user.
         """
         status_msg = state.get("status_msg", None)
@@ -589,10 +741,13 @@ class PresenceHandler(BaseHandler):
         prev_state = yield self.current_state_for_user(user_id)
 
         new_fields = {
-            "state": presence,
-            "status_msg": status_msg if presence != PresenceState.OFFLINE else None
+            "state": presence
         }
 
+        if not ignore_status_msg:
+            msg = status_msg if presence != PresenceState.OFFLINE else None
+            new_fields["status_msg"] = msg
+
         if presence == PresenceState.ONLINE:
             new_fields["last_active_ts"] = self.clock.time_msec()
 
@@ -611,14 +766,14 @@ class PresenceHandler(BaseHandler):
         # don't need to send to local clients here, as that is done as part
         # of the event stream/sync.
         # TODO: Only send to servers not already in the room.
-        if self.hs.is_mine(user):
+        user_ids = yield self.state.get_current_user_in_room(room_id)
+        if self.is_mine(user):
             state = yield self.current_state_for_user(user.to_string())
 
-            hosts = yield self.store.get_joined_hosts_for_room(room_id)
+            hosts = set(get_domain_from_id(u) for u in user_ids)
             self._push_to_remotes({host: (state,) for host in hosts})
         else:
-            user_ids = yield self.store.get_users_in_room(room_id)
-            user_ids = filter(self.hs.is_mine_id, user_ids)
+            user_ids = filter(self.is_mine_id, user_ids)
 
             states = yield self.current_state_for_users(user_ids)
 
@@ -628,7 +783,7 @@ class PresenceHandler(BaseHandler):
     def get_presence_list(self, observer_user, accepted=None):
         """Returns the presence for all users in their presence list.
         """
-        if not self.hs.is_mine(observer_user):
+        if not self.is_mine(observer_user):
             raise SynapseError(400, "User is not hosted on this Home Server")
 
         presence_list = yield self.store.get_presence_list(
@@ -659,7 +814,7 @@ class PresenceHandler(BaseHandler):
             observer_user.localpart, observed_user.to_string()
         )
 
-        if self.hs.is_mine(observed_user):
+        if self.is_mine(observed_user):
             yield self.invite_presence(observed_user, observer_user)
         else:
             yield self.federation.send_edu(
@@ -675,11 +830,11 @@ class PresenceHandler(BaseHandler):
     def invite_presence(self, observed_user, observer_user):
         """Handles new presence invites.
         """
-        if not self.hs.is_mine(observed_user):
+        if not self.is_mine(observed_user):
             raise SynapseError(400, "User is not hosted on this Home Server")
 
         # TODO: Don't auto accept
-        if self.hs.is_mine(observer_user):
+        if self.is_mine(observer_user):
             yield self.accept_presence(observed_user, observer_user)
         else:
             self.federation.send_edu(
@@ -742,7 +897,7 @@ class PresenceHandler(BaseHandler):
         Returns:
             A Deferred.
         """
-        if not self.hs.is_mine(observer_user):
+        if not self.is_mine(observer_user):
             raise SynapseError(400, "User is not hosted on this Home Server")
 
         yield self.store.del_presence_list(
@@ -793,28 +948,38 @@ class PresenceHandler(BaseHandler):
 def should_notify(old_state, new_state):
     """Decides if a presence state change should be sent to interested parties.
     """
+    if old_state == new_state:
+        return False
+
     if old_state.status_msg != new_state.status_msg:
+        notify_reason_counter.inc("status_msg_change")
         return True
 
-    if old_state.state == PresenceState.ONLINE:
-        if new_state.state != PresenceState.ONLINE:
-            # Always notify for online -> anything
-            return True
+    if old_state.state != new_state.state:
+        notify_reason_counter.inc("state_change")
+        state_transition_counter.inc(old_state.state, new_state.state)
+        return True
 
+    if old_state.state == PresenceState.ONLINE:
         if new_state.currently_active != old_state.currently_active:
+            notify_reason_counter.inc("current_active_change")
             return True
 
-    if new_state.last_active_ts - old_state.last_active_ts > LAST_ACTIVE_GRANULARITY:
-        # Always notify for a transition where last active gets bumped.
-        return True
+        if new_state.last_active_ts - old_state.last_active_ts > LAST_ACTIVE_GRANULARITY:
+            # Only notify about last active bumps if we're not currently acive
+            if not new_state.currently_active:
+                notify_reason_counter.inc("last_active_change_online")
+                return True
 
-    if old_state.state != new_state.state:
+    elif new_state.last_active_ts - old_state.last_active_ts > LAST_ACTIVE_GRANULARITY:
+        # Always notify for a transition where last active gets bumped.
+        notify_reason_counter.inc("last_active_change_not_online")
         return True
 
     return False
 
 
-def _format_user_presence_state(state, now):
+def format_user_presence_state(state, now):
     """Convert UserPresenceState to a format that can be sent down to clients
     and to other servers.
     """
@@ -834,9 +999,14 @@ def _format_user_presence_state(state, now):
 
 class PresenceEventSource(object):
     def __init__(self, hs):
-        self.hs = hs
+        # We can't call get_presence_handler here because there's a cycle:
+        #
+        #   Presence -> Notifier -> PresenceEventSource -> Presence
+        #
+        self.get_presence_handler = hs.get_presence_handler
         self.clock = hs.get_clock()
         self.store = hs.get_datastore()
+        self.state = hs.get_state_handler()
 
     @defer.inlineCallbacks
     @log_function
@@ -860,7 +1030,7 @@ class PresenceEventSource(object):
                 from_key = int(from_key)
             room_ids = room_ids or []
 
-            presence = self.hs.get_handlers().presence_handler
+            presence = self.get_presence_handler()
             stream_change_cache = self.store.presence_stream_cache
 
             if not room_ids:
@@ -877,13 +1047,13 @@ class PresenceEventSource(object):
 
             user_ids_changed = set()
             changed = None
-            if from_key and max_token - from_key < 100:
-                # For small deltas, its quicker to get all changes and then
-                # work out if we share a room or they're in our presence list
+            if from_key:
                 changed = stream_change_cache.get_all_entities_changed(from_key)
 
-            # get_all_entities_changed can return None
-            if changed is not None:
+            if changed is not None and len(changed) < 500:
+                # For small deltas, its quicker to get all changes and then
+                # work out if we share a room or they're in our presence list
+                get_updates_counter.inc("stream")
                 for other_user_id in changed:
                     if other_user_id in friends:
                         user_ids_changed.add(other_user_id)
@@ -895,9 +1065,11 @@ class PresenceEventSource(object):
             else:
                 # Too many possible updates. Find all users we can see and check
                 # if any of them have changed.
+                get_updates_counter.inc("full")
+
                 user_ids_to_check = set()
                 for room_id in room_ids:
-                    users = yield self.store.get_users_in_room(room_id)
+                    users = yield self.state.get_current_user_in_room(room_id)
                     user_ids_to_check.update(users)
 
                 user_ids_to_check.update(friends)
@@ -920,7 +1092,7 @@ class PresenceEventSource(object):
         defer.returnValue(([
             {
                 "type": "m.presence",
-                "content": _format_user_presence_state(s, now),
+                "content": format_user_presence_state(s, now),
             }
             for s in updates.values()
             if include_offline or s.state != PresenceState.OFFLINE
@@ -933,15 +1105,14 @@ class PresenceEventSource(object):
         return self.get_new_events(user, from_key=None, include_offline=False)
 
 
-def handle_timeouts(user_states, is_mine_fn, user_to_num_current_syncs, now):
+def handle_timeouts(user_states, is_mine_fn, syncing_user_ids, now):
     """Checks the presence of users that have timed out and updates as
     appropriate.
 
     Args:
         user_states(list): List of UserPresenceState's to check.
         is_mine_fn (fn): Function that returns if a user_id is ours
-        user_to_num_current_syncs (dict): Mapping of user_id to number of currently
-            active syncs.
+        syncing_user_ids (set): Set of user_ids with active syncs.
         now (int): Current time in ms.
 
     Returns:
@@ -952,21 +1123,20 @@ def handle_timeouts(user_states, is_mine_fn, user_to_num_current_syncs, now):
     for state in user_states:
         is_mine = is_mine_fn(state.user_id)
 
-        new_state = handle_timeout(state, is_mine, user_to_num_current_syncs, now)
+        new_state = handle_timeout(state, is_mine, syncing_user_ids, now)
         if new_state:
             changes[state.user_id] = new_state
 
     return changes.values()
 
 
-def handle_timeout(state, is_mine, user_to_num_current_syncs, now):
+def handle_timeout(state, is_mine, syncing_user_ids, now):
     """Checks the presence of the user to see if any of the timers have elapsed
 
     Args:
         state (UserPresenceState)
         is_mine (bool): Whether the user is ours
-        user_to_num_current_syncs (dict): Mapping of user_id to number of currently
-            active syncs.
+        syncing_user_ids (set): Set of user_ids with active syncs.
         now (int): Current time in ms.
 
     Returns:
@@ -1000,7 +1170,7 @@ def handle_timeout(state, is_mine, user_to_num_current_syncs, now):
 
         # If there are have been no sync for a while (and none ongoing),
         # set presence to offline
-        if not user_to_num_current_syncs.get(user_id, 0):
+        if user_id not in syncing_user_ids:
             if now - state.last_user_sync_ts > SYNC_ONLINE_TIMEOUT:
                 state = state.copy_and_replace(
                     state=PresenceState.OFFLINE,