Prevent operating on swapped out map. (#3670)

* Prevent operating on swapped out map.

* test

pkg/rtc/room.go

@@ -1338,14 +1338,15 @@ func (r *Room) broadcastParticipantState(p types.LocalParticipant, opts broadcas
 		return
 	}
 
+	r.batchedUpdatesMu.Lock()
 	updates := PushAndDequeueUpdates(
 		pi,
 		p.CloseReason(),
 		opts.immediate,
 		r.GetParticipant(livekit.ParticipantIdentity(pi.Identity)),
-		&r.batchedUpdatesMu,
 		r.batchedUpdates,
 	)
+	r.batchedUpdatesMu.Unlock()
 	if len(updates) != 0 {
 		selfSent = true
 		SendParticipantUpdates(updates, r.GetParticipants())
@@ -1395,14 +1396,14 @@ func (r *Room) changeUpdateWorker() {
 			r.sendRoomUpdate()
 		case <-subTicker.C:
 			r.batchedUpdatesMu.Lock()
+			if len(r.batchedUpdates) == 0 {
+				r.batchedUpdatesMu.Unlock()
+				continue
+			}
 			updatesMap := r.batchedUpdates
 			r.batchedUpdates = make(map[livekit.ParticipantIdentity]*ParticipantUpdate)
 			r.batchedUpdatesMu.Unlock()
 
-			if len(updatesMap) == 0 {
-				continue
-			}
-
 			SendParticipantUpdates(maps.Values(updatesMap), r.GetParticipants())
 		}
 	}
@@ -1819,12 +1820,8 @@ func PushAndDequeueUpdates(
 	closeReason types.ParticipantCloseReason,
 	isImmediate bool,
 	existingParticipant types.Participant,
-	lock *sync.Mutex,
 	cache map[livekit.ParticipantIdentity]*ParticipantUpdate,
 ) []*ParticipantUpdate {
-	lock.Lock()
-	defer lock.Unlock()
-
 	var updates []*ParticipantUpdate
 	identity := livekit.ParticipantIdentity(pi.Identity)
 	existing := cache[identity]

pkg/rtc/room_test.go

@@ -351,14 +351,15 @@ func TestPushAndDequeueUpdates(t *testing.T) {
 			if tc.existing != nil {
 				rm.batchedUpdates[livekit.ParticipantIdentity(tc.existing.ParticipantInfo.Identity)] = tc.existing
 			}
+			rm.batchedUpdatesMu.Lock()
 			updates := PushAndDequeueUpdates(
 				tc.pi,
 				tc.closeReason,
 				tc.immediate,
 				rm.GetParticipant(livekit.ParticipantIdentity(tc.pi.Identity)),
-				&rm.batchedUpdatesMu,
 				rm.batchedUpdates,
 			)
+			rm.batchedUpdatesMu.Unlock()
 			require.Equal(t, len(tc.expected), len(updates))
 			for i, item := range tc.expected {
 				requirePIEquals(t, item.ParticipantInfo, updates[i].ParticipantInfo)