add lock for refresh operation

Author: zhiyuanliang-ms

src/AzureAppConfigurationImpl.ts

@@ -9,6 +9,7 @@ import { IKeyValueAdapter } from "./IKeyValueAdapter.js";
 import { JsonKeyValueAdapter } from "./JsonKeyValueAdapter.js";
 import { DEFAULT_REFRESH_INTERVAL_IN_MS, MIN_REFRESH_INTERVAL_IN_MS } from "./RefreshOptions.js";
 import { Disposable } from "./common/disposable.js";
+import { Lock } from "./common/lock.js"
 import { FEATURE_FLAGS_KEY_NAME, FEATURE_MANAGEMENT_KEY_NAME } from "./featureManagement/constants.js";
 import { AzureKeyVaultKeyValueAdapter } from "./keyvault/AzureKeyVaultKeyValueAdapter.js";
 import { RefreshTimer } from "./refresh/RefreshTimer.js";
@@ -40,6 +41,8 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
     #isInitialLoadCompleted: boolean = false;
 
     // Refresh
+    #refreshLock: Lock = new Lock(); // lock to prevent "concurrent" async refresh
+
     #refreshInterval: number = DEFAULT_REFRESH_INTERVAL_IN_MS;
     #onRefreshListeners: Array<() => any> = [];
     /**
@@ -350,6 +353,10 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
             throw new Error("Refresh is not enabled for key-values or feature flags.");
         }
 
+        this.#refreshLock.execute(this.#refreshTasks);
+    }
+
+    async #refreshTasks(): Promise<void> {
         const refreshTasks: Promise<boolean>[] = [];
         if (this.#refreshEnabled) {
             refreshTasks.push(this.#refreshKeyValues());

src/common/lock.ts

@@ -0,0 +1,18 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+
+export class Lock {
+    #locked = false;
+
+    async execute(fn) {
+        if (this.#locked) {
+            return; // do nothing
+        }
+        this.#locked = true;
+        try {
+            await fn();
+        } finally {
+            this.#locked = false;
+        }
+    }
+}