Add mutex protection to checkAndTriggerSubscriptionChanged

Motivation: there is a race condition where it is possible for the app state to be the same when this function fires twice. Even though the function is async, we need it to run synchronously to ensure that each operation is fully completed before the next begins, thus preserving the integrity and consistency of the application state.

Author: rgomezp

src/helpers/EventHelper.ts

@@ -11,34 +11,52 @@ import LocalStorage from '../utils/LocalStorage';
 import { CustomLinkManager } from '../managers/CustomLinkManager';
 
 export default class EventHelper {
-  static onNotificationPermissionChange() {
-    EventHelper.checkAndTriggerSubscriptionChanged();
+  static _mutexPromise: Promise<void> = Promise.resolve();
+  static _mutexLocked = false;
+
+  static async onNotificationPermissionChange() {
+    await EventHelper.checkAndTriggerSubscriptionChanged();
   }
 
   static async onInternalSubscriptionSet(optedOut: boolean) {
     LimitStore.put('subscription.optedOut', optedOut);
   }
 
   static async checkAndTriggerSubscriptionChanged() {
-    OneSignalUtils.logMethodCall('checkAndTriggerSubscriptionChanged');
-    const context: ContextSWInterface = OneSignal.context;
-    const subscriptionState = await context.subscriptionManager.getSubscriptionState();
-    const isPushEnabled = await OneSignal.privateIsPushNotificationsEnabled();
-    const appState = await Database.getAppState();
-    const { lastKnownPushEnabled } = appState;
-    const didStateChange = (
-      lastKnownPushEnabled === null ||
-      isPushEnabled !== lastKnownPushEnabled
-    );
-    if (!didStateChange) return;
-    Log.info(
-      `The user's subscription state changed from ` +
-        `${lastKnownPushEnabled === null ? '(not stored)' : lastKnownPushEnabled} ⟶ ${subscriptionState.subscribed}`
-    );
-    LocalStorage.setIsPushNotificationsEnabled(isPushEnabled);
-    appState.lastKnownPushEnabled = isPushEnabled;
-    await Database.setAppState(appState);
-    EventHelper.triggerSubscriptionChanged(isPushEnabled);
+    if (EventHelper._mutexLocked) {
+      await EventHelper._mutexPromise;
+    }
+
+    EventHelper._mutexLocked = true;
+    // eslint-disable-next-line no-async-promise-executor
+    EventHelper._mutexPromise = new Promise(async (resolve, reject) => {
+      try {
+        OneSignalUtils.logMethodCall('checkAndTriggerSubscriptionChanged');
+        const context: ContextSWInterface = OneSignal.context;
+        const subscriptionState = await context.subscriptionManager.getSubscriptionState();
+        const isPushEnabled = await OneSignal.privateIsPushNotificationsEnabled();
+        const appState = await Database.getAppState();
+        const { lastKnownPushEnabled } = appState;
+        const didStateChange = (
+          lastKnownPushEnabled === null ||
+          isPushEnabled !== lastKnownPushEnabled
+        );
+        if (!didStateChange) return;
+        Log.info(
+          `The user's subscription state changed from ` +
+            `${lastKnownPushEnabled === null ? '(not stored)' : lastKnownPushEnabled} ⟶ ${subscriptionState.subscribed}`
+        );
+        LocalStorage.setIsPushNotificationsEnabled(isPushEnabled);
+        appState.lastKnownPushEnabled = isPushEnabled;
+        await Database.setAppState(appState);
+        EventHelper.triggerSubscriptionChanged(isPushEnabled);
+        EventHelper._mutexLocked = false;
+        resolve();
+      } catch (e) {
+        EventHelper._mutexLocked = false;
+        reject(`checkAndTriggerSubscriptionChanged error: ${e}`);
+      }
+    });
   }
 
   static async _onSubscriptionChanged(newSubscriptionState: boolean | undefined) {

test/unit/public-sdk-apis/onSession.ts

@@ -18,6 +18,7 @@ import {
 import { createSubscription } from "../../support/tester/utils";
 import EventsTestHelper from '../../support/tester/EventsTestHelper';
 import { DelayedPromptType } from '../../../src/models/Prompts';
+import EventHelper from "../../../src/helpers/EventHelper";
 
 
 const sinonSandbox: SinonSandbox = sinon.sandbox.create();
@@ -30,6 +31,8 @@ test.afterEach(function (_t: ExecutionContext) {
   OneSignal._initCalled = false;
   OneSignal.__initAlreadyCalled = false;
   OneSignal._sessionInitAlreadyRunning = false;
+  EventHelper._mutexPromise = Promise.resolve();
+  EventHelper._mutexLocked = false;
 });
 
 /**