Initial support for job queue

ts/test-both/AsyncQueue_test.ts

@@ -0,0 +1,36 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+/* eslint-disable no-restricted-syntax */
+
+import { assert } from 'chai';
+
+import { AsyncQueue } from '../util/AsyncQueue';
+
+describe('AsyncQueue', () => {
+  it('yields values as they are added, even if they were added before consuming', async () => {
+    const queue = new AsyncQueue<number>();
+
+    queue.add(1);
+    queue.add(2);
+
+    const resultPromise = (async () => {
+      const results = [];
+      for await (const value of queue) {
+        results.push(value);
+        if (value === 4) {
+          break;
+        }
+      }
+      return results;
+    })();
+
+    queue.add(3);
+    queue.add(4);
+
+    // Ignored, because we should've stopped iterating.
+    queue.add(5);
+
+    assert.deepEqual(await resultPromise, [1, 2, 3, 4]);
+  });
+});