Bug 1705720 - Ensure the dispatcher is always available

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 [Full changelog](https://github.com/mozilla/glean.js/compare/v0.10.0...main)
 
+* [#254](https://github.com/mozilla/glean.js/pull/254): BUGFIX: Allow the usage of the Glean specific metrics API before Glean is initialized.
+
 # v0.10.0 (2021-04-20)
 
 [Full changelog](https://github.com/mozilla/glean.js/compare/v0.9.2...v0.10.0)

glean/src/core/context.ts

@@ -3,7 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 import type { DebugOptions } from "./debug_options";
-import type Dispatcher from "./dispatcher";
+import Dispatcher from "./dispatcher";
 import type MetricsDatabase from "./metrics/database";
 import type EventsDatabase from "./metrics/events_database";
 import type PingsDatabase from "./pings/database";
@@ -23,21 +23,20 @@ import type PingsDatabase from "./pings/database";
 export class Context {
   private static _instance: Context;
 
-  private _dispatcher!: Dispatcher;
+  private _dispatcher!: Dispatcher | null;
 
   private _uploadEnabled!: boolean;
   private _metricsDatabase!: MetricsDatabase;
   private _eventsDatabase!: EventsDatabase;
   private _pingsDatabase!: PingsDatabase;
 
   private _applicationId!: string;
-  private _initialized!: boolean;
+  private _initialized: boolean;
 
   private _debugOptions!: DebugOptions;
 
   private constructor() {
-    // Intentionally empty, exclusively defined to mark the
-    // constructor as private.
+    this._initialized = false;
   }
 
   static get instance(): Context {
@@ -48,7 +47,33 @@ export class Context {
     return Context._instance;
   }
 
+  /**
+   * **Test-only API**
+   *
+   * Resets the Context to an uninitialized state.
+   */
+  static async testUninitialize(): Promise<void> {
+    // Clear the dispatcher queue and return the dispatcher back to an uninitialized state.
+    if (Context.instance._dispatcher) {
+      await Context.instance._dispatcher.testUninitialize();
+    }
+
+    // Due to the test requirement of keeping storage in place,
+    // we can't simply wipe out the full `Context` instance.
+    // The closest thing we can do is making the dispatcher `null`.
+    Context.instance._dispatcher = null;
+    Context.initialized = false;
+  }
+
   static get dispatcher(): Dispatcher {
+    // Create a dispatcher if one isn't available already.
+    // This is required since the dispatcher may be used
+    // earlier than Glean initialization, so we can't rely
+    // on `Glean.initialize` to set it.
+    if (!Context.instance._dispatcher) {
+      Context.instance._dispatcher = new Dispatcher();
+    }
+
     return Context.instance._dispatcher;
   }
 

glean/src/core/glean.ts

@@ -14,7 +14,6 @@ import EventsDatabase from "./metrics/events_database.js";
 import UUIDMetricType from "./metrics/types/uuid.js";
 import DatetimeMetricType from "./metrics/types/datetime.js";
 import { DatetimeMetric } from "./metrics/types/datetime_metric.js";
-import Dispatcher from "./dispatcher.js";
 import CorePings from "./internal_pings.js";
 import { registerPluginToEvent, testResetEvents } from "./events/utils.js";
 
@@ -51,10 +50,8 @@ class Glean {
       Use Glean.instance instead to access the Glean singleton.`);
     }
 
-    Context.dispatcher = new Dispatcher();
     this._coreMetrics = new CoreMetrics();
     this._corePings = new CorePings();
-    Context.initialized = false;
   }
 
   private static get instance(): Glean {
@@ -501,16 +498,11 @@ class Glean {
    */
   static async testUninitialize(): Promise<void> {
     // Get back to an uninitialized state.
-    Context.initialized = false;
+    await Context.testUninitialize();
 
     // Deregister all plugins
     testResetEvents();
 
-    // Clear the dispatcher queue and return the dispatcher back to an uninitialized state.
-    if (Context.dispatcher) {
-      await Context.dispatcher.testUninitialize();
-    }
-
     // Stop ongoing jobs and clear pending pings queue.
     if (Glean.pingUploader) {
       // The first time tests run, before Glean is initialized, we are

glean/tests/core/context.spec.ts

@@ -68,4 +68,20 @@ describe("Context", function() {
     assert.notStrictEqual(Context.pingsDatabase, undefined);
     assert.ok(Context.pingsDatabase instanceof PingsDatabase);
   });
+
+  it("the dispatcher is always available", async function () {
+    const originalDispatcher = Context.dispatcher;
+    assert.notStrictEqual(originalDispatcher, null);
+
+    await Context.testUninitialize();
+
+    // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+    // @ts-ignore
+    assert.strictEqual(Context.instance._dispatcher, null);
+
+    // Trying to access the dispatcher will instantiate a new one.
+    const newDispatcher = Context.instance;
+    assert.notStrictEqual(newDispatcher, null);
+    assert.notStrictEqual(newDispatcher, originalDispatcher);
+  });
 });