[Fix] Watched Queries Race Condition

.changeset/eleven-moons-sit.md

@@ -0,0 +1,5 @@
+---
+'@journeyapps/powersync-sdk-web': patch
+---
+
+Fixed watched queries not updating due to race condition when opening multiple WA-SQLite connections due to initiating multiple PowerSync instances simultaneously.

packages/powersync-sdk-web/src/worker/db/SharedWASQLiteDB.worker.ts

@@ -6,24 +6,30 @@ import { DBWorkerInterface, _openDB } from './open-db';
 
 const _self: SharedWorkerGlobalScope = self as any;
 
-const DBMap = new Map<string, DBWorkerInterface>();
+const DBMap = new Map<string, Promise<DBWorkerInterface>>();
 
 const openDB = async (dbFileName: string): Promise<DBWorkerInterface> => {
   if (!DBMap.has(dbFileName)) {
-    DBMap.set(dbFileName, await _openDB(dbFileName));
+    const openPromise = _openDB(dbFileName);
+    DBMap.set(dbFileName, openPromise);
+    openPromise.catch((error) => {
+      // Allow for retries if an error ocurred
+      console.error(error);
+      DBMap.delete(dbFileName);
+    });
   }
-  return Comlink.proxy(DBMap.get(dbFileName)!);
+  return Comlink.proxy(await DBMap.get(dbFileName)!);
 };
 
 _self.onconnect = function (event: MessageEvent<string>) {
   const port = event.ports[0];
-
   console.debug('Exposing db on port', port);
   Comlink.expose(openDB, port);
 };
 
 addEventListener('beforeunload', (event) => {
-  Array.from(DBMap.values()).forEach((db) => {
+  Array.from(DBMap.values()).forEach(async (dbPromise) => {
+    const db = await dbPromise;
     db.close?.();
   });
 });

packages/powersync-sdk-web/src/worker/db/open-db.ts

@@ -24,8 +24,6 @@ export type WASQLiteExecuteMethod = (sql: string, params?: any[]) => Promise<WAS
 export type OnTableChangeCallback = (opType: number, tableName: string, rowId: number) => void;
 export type OpenDB = (dbFileName: string) => DBWorkerInterface;
 
-const listeners = new Map<string, OnTableChangeCallback>();
-
 export async function _openDB(dbFileName: string): Promise<DBWorkerInterface> {
   const { default: moduleFactory } = await import('@journeyapps/wa-sqlite/dist/wa-sqlite-async.mjs');
   const module = await moduleFactory();
@@ -37,6 +35,11 @@ export async function _openDB(dbFileName: string): Promise<DBWorkerInterface> {
 
   const db = await sqlite3.open_v2(dbFileName);
 
+  /**
+   * Listeners are exclusive to the DB connection.
+   */
+  const listeners = new Map<string, OnTableChangeCallback>();
+
   sqlite3.register_table_onchange_hook(db, (opType: number, tableName: string, rowId: number) => {
     Array.from(listeners.values()).forEach((l) => l(opType, tableName, rowId));
   });