Allow simultaneous adds

src/matrix/room/BaseRoom.js

@@ -300,9 +300,7 @@ export class BaseRoom extends EventEmitter {
             await decryptRequest.complete();
         }
         // once txn is committed, update in-memory state & emit events
-        for (const fragment of gapResult.fragments) {
-            this._fragmentIdComparer.add(fragment);
-        }
+        this._fragmentIdComparer.add(...gapResult.fragments);
         if (extraGapFillChanges) {
             this._applyGapFill(extraGapFillChanges);
         }

src/matrix/room/timeline/FragmentIdComparer.js

@@ -171,9 +171,11 @@ export class FragmentIdComparer {
     }
 
     /** use for fragments coming out of persistence, not newly created ones, or also fragments for a new island (like for a permalink) */
-    add(fragment) {
+    add(...fragments) {
+        for (const fragment of fragments) {
             const copy = new Fragment(fragment.id, fragment.previousId, fragment.nextId);
             this._fragmentsById.set(fragment.id, copy);
+        }
         this.rebuild(this._fragmentsById.values());
     }