refactor: make sure promises are settled before app shutdown (#12942)

👍

packages/backend/src/misc/promise-tracker.ts

@@ -0,0 +1,23 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and other misskey contributors
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+const promiseRefs: Set<WeakRef<Promise<unknown>>> = new Set();
+
+/**
+ * This tracks promises that other modules decided not to wait for,
+ * and makes sure they are all settled before fully closing down the server.
+ */
+export function trackPromise(promise: Promise<unknown>) {
+	if (process.env.NODE_ENV !== 'test') {
+		return;
+	}
+	const ref = new WeakRef(promise);
+	promiseRefs.add(ref);
+	promise.finally(() => promiseRefs.delete(ref));
+}
+
+export async function allSettled(): Promise<void> {
+	await Promise.allSettled([...promiseRefs].map(r => r.deref()));
+}