Fix intermittently failing test

js/worker-threads/src/index.test.ts

@@ -781,10 +781,13 @@ describe("WorkerThreads", () => {
       }
     );
 
-    it("retries a task once when its reused thread dies before starting it", async () => {
+    it("retries a task once when its reused thread dies before starting it", async ({
+      onTestFinished,
+    }) => {
       const executor = new WorkerThreads({ maxThreads: 1 });
+      onTestFinished(() => executor.close());
       const exiting = executor.handler(testJob, {
-        exportName: "blockThenExit",
+        exportName: "exitBeforeNextTask",
         module: handlers,
       });
       const complete = executor.handler(testJob, {
@@ -805,7 +808,6 @@ describe("WorkerThreads", () => {
         crashedThreads: 1,
         totalThreads: 1,
       });
-      await executor.close();
     });
 
     it("fails an attempt that exceeds its thread's heap limit", async () => {

js/worker-threads/src/testdata/handlers.ts

@@ -5,6 +5,8 @@
  * the TypeScript source, so every test also exercises the thread's fallback
  * from a missing `.js` module to its `.ts` source.
  */
+import { parentPort } from "node:worker_threads";
+
 import {
   complete as completeOutcome,
   snooze as snoozeOutcome,
@@ -22,19 +24,6 @@ export const allocateForever: TestHandler = ({ logger }) => {
   for (;;) retained.push(new Array<number>(100_000).fill(retained.length));
 };
 
-export const blockThenExit: TestHandler = () => {
-  // Keep the thread busy after returning so the next run message is queued
-  // behind this callback, then exit before the thread can acknowledge it.
-  setImmediate(() => {
-    const end = Date.now() + 100;
-    while (Date.now() < end) {
-      // Deliberately block this isolated thread.
-    }
-    process.exit(9);
-  });
-  return completeOutcome();
-};
-
 export const complete: TestHandler = ({ job }) =>
   completeOutcome({ output: { value: job.args.value ?? null } });
 
@@ -93,6 +82,14 @@ export const echoExact: TestHandler = ({
   return completeOutcome({ output: { id } });
 };
 
+export const exitBeforeNextTask: TestHandler = () => {
+  // Replace the run listener so the next task kills this thread before it
+  // can acknowledge the task. A setImmediate callback races with that message.
+  parentPort?.removeAllListeners("message");
+  parentPort?.once("message", () => process.exit(9));
+  return completeOutcome();
+};
+
 export const exitWhenIdle: TestHandler = () => {
   setImmediate(() => process.exit(7));
   return completeOutcome();