Fix another freeze on room switch (#7900)

* Fix another freeze on room switch

This switches permalinks to use the batch state update event and
removes the incremental updates, as commented. We now spend, on my
profiling, about 450ms in setOutOfBandMembers itself and another
120ms in permalinks.

Fixes element-hq/element-web#21127

* Just bind to the currentstate state updates

src/utils/permalinks/Permalinks.ts

@@ -15,12 +15,8 @@ limitations under the License.
 */
 
 import isIp from "is-ip";
-import { throttle } from "lodash";
 import * as utils from "matrix-js-sdk/src/utils";
 import { Room } from "matrix-js-sdk/src/models/room";
-import { EventType } from "matrix-js-sdk/src/@types/event";
-import { MatrixEvent } from "matrix-js-sdk/src/models/event";
-import { RoomMember, RoomMemberEvent } from "matrix-js-sdk/src/models/room-member";
 import { logger } from "matrix-js-sdk/src/logger";
 import { RoomStateEvent } from "matrix-js-sdk/src/models/room-state";
 
@@ -108,15 +104,9 @@ export class RoomPermalinkCreator {
         if (!this.roomId) {
             throw new Error("Failed to resolve a roomId for the permalink creator to use");
         }
-
-        if (shouldThrottle) {
-            this.updateServerCandidates = throttle(
-                this.updateServerCandidates, 200, { leading: true, trailing: true },
-            );
-        }
     }
 
-    load() {
+    public load() {
         if (!this.room || !this.room.currentState) {
             // Under rare and unknown circumstances it is possible to have a room with no
             // currentState, at least potentially at the early stages of joining a room.
@@ -125,38 +115,33 @@ export class RoomPermalinkCreator {
             logger.warn("Tried to load a permalink creator with no room state");
             return;
         }
-        this.updateAllowedServers();
-        this.updateHighestPlUser();
-        this.updatePopulationMap();
-        this.updateServerCandidates();
+        this.fullUpdate();
     }
 
-    start() {
+    public start() {
         this.load();
-        this.room.client.on(RoomMemberEvent.Membership, this.onMembership);
-        this.room.currentState.on(RoomStateEvent.Events, this.onRoomState);
+        this.room.currentState.on(RoomStateEvent.Update, this.onRoomStateUpdate);
         this.started = true;
     }
 
-    stop() {
-        this.room.client.removeListener(RoomMemberEvent.Membership, this.onMembership);
-        this.room.currentState.removeListener(RoomStateEvent.Events, this.onRoomState);
+    public stop() {
+        this.room.currentState.removeListener(RoomStateEvent.Update, this.onRoomStateUpdate);
         this.started = false;
     }
 
-    get serverCandidates() {
+    public get serverCandidates() {
         return this._serverCandidates;
     }
 
-    isStarted() {
+    public isStarted() {
         return this.started;
     }
 
-    forEvent(eventId: string): string {
+    public forEvent(eventId: string): string {
         return getPermalinkConstructor().forEvent(this.roomId, eventId, this._serverCandidates);
     }
 
-    forShareableRoom(): string {
+    public forShareableRoom(): string {
         if (this.room) {
             // Prefer to use canonical alias for permalink if possible
             const alias = this.room.getCanonicalAlias();
@@ -167,43 +152,28 @@ export class RoomPermalinkCreator {
         return getPermalinkConstructor().forRoom(this.roomId, this._serverCandidates);
     }
 
-    forRoom(): string {
+    public forRoom(): string {
         return getPermalinkConstructor().forRoom(this.roomId, this._serverCandidates);
     }
 
-    private onRoomState = (event: MatrixEvent) => {
-        switch (event.getType()) {
-            case EventType.RoomServerAcl:
-                this.updateAllowedServers();
-                this.updateHighestPlUser();
-                this.updatePopulationMap();
-                this.updateServerCandidates();
-                return;
-            case EventType.RoomPowerLevels:
-                this.updateHighestPlUser();
-                this.updateServerCandidates();
-                return;
-        }
+    private onRoomStateUpdate = () => {
+        this.fullUpdate();
     };
 
-    private onMembership = (evt: MatrixEvent, member: RoomMember, oldMembership: string) => {
-        if (member.roomId !== this.room.roomId) return;
-
-        const userId = member.userId;
-        const membership = member.membership;
-        const serverName = getServerName(userId);
-        const hasJoined = oldMembership !== "join" && membership === "join";
-        const hasLeft = oldMembership === "join" && membership !== "join";
-
-        if (hasLeft) {
-            this.populationMap[serverName]--;
-        } else if (hasJoined) {
-            this.populationMap[serverName]++;
-        }
-
+    private fullUpdate() {
+        // This updates the internal state of this object from the room state. It's broken
+        // down into separate functions, previously because we did some of these as incremental
+        // updates, but they were on member events which can be very numerous, so the incremental
+        // updates ended up being much slower than a full update. We now have the batch state update
+        // event, so we just update in full, but on each batch of updates.
+        // A full update takes about 120ms for me on Matrix HQ, which still feels like way too long
+        // to be spending worrying about how we might generate a permalink, but it's better than
+        // multiple seconds.
+        this.updateAllowedServers();
         this.updateHighestPlUser();
+        this.updatePopulationMap();
         this.updateServerCandidates();
-    };
+    }
 
     private updateHighestPlUser() {
         const plEvent = this.room.currentState.getStateEvents("m.room.power_levels", "");

test/utils/permalinks/Permalinks-test.js

@@ -122,14 +122,14 @@ describe('Permalinks', function() {
             },
             member95,
         ]);
-        const creator = new RoomPermalinkCreator(room, null, false);
+        const creator = new RoomPermalinkCreator(room, null);
         creator.load();
         expect(creator._serverCandidates[0]).toBe("pl_95");
         member95.membership = "left";
-        creator.onMembership({}, member95, "join");
+        creator.onRoomStateUpdate();
         expect(creator._serverCandidates[0]).toBe("pl_75");
         member95.membership = "join";
-        creator.onMembership({}, member95, "left");
+        creator.onRoomStateUpdate();
         expect(creator._serverCandidates[0]).toBe("pl_95");
     });