[miniflare] fix: ensure Mutex doesn't report itself as drained if locked

.changeset/rude-chicken-raise.md

@@ -0,0 +1,13 @@
+---
+"miniflare": patch
+---
+
+fix: ensure `Mutex` doesn't report itself as drained if locked
+
+Previously, Miniflare's `Mutex` implementation would report itself as drained
+if there were no waiters, regardless of the locked state. This bug meant that
+if you called but didn't `await` `Miniflare#setOptions()`, future calls to
+`Miniflare#dispatchFetch()` (or any other asynchronous `Miniflare` method)
+wouldn't wait for the options update to apply and the runtime to restart before
+sending requests. This change ensures we wait until the mutex is unlocked before
+reporting it as drained.

packages/miniflare/src/workers/shared/sync.ts

@@ -71,7 +71,7 @@ export class Mutex {
 	}
 
 	async drained(): Promise<void> {
-		if (this.resolveQueue.length === 0) return;
+		if (this.resolveQueue.length === 0 && !this.locked) return;
 		return new Promise((resolve) => this.drainQueue.push(resolve));
 	}
 }

packages/miniflare/test/shared/sync.spec.ts

@@ -46,6 +46,7 @@ test("Mutex: maintains separate drain queue", async (t) => {
 	void mutex.runWith(() => deferred1);
 	let drained = false;
 	mutex.drained().then(() => (drained = true));
+	await setTimeout();
 	t.false(drained);
 	deferred1.resolve();
 	await setTimeout();
@@ -64,6 +65,7 @@ test("Mutex: maintains separate drain queue", async (t) => {
 	});
 	drained = false;
 	mutex.drained().then(() => (drained = true));
+	await setTimeout();
 	t.false(drained);
 	deferred2.resolve();
 	await setTimeout();