--detectOpenHandles shouldn't report unreferenced workers.

[nicolo-ribaudo]

🐛 Bug Report

Node.js workers have an .unref() method that, when called, makes them not prevent the main thread from exiting. It's similar to setTimeout().unref().

If a worker has been .unref()ed, Jest shouldn't report it in --detectOpenHandles. This is siilar to #8941

To Reproduce

I have two file: test.js and worker.js (I tested them in a bigger repository; if needed I'll create a self-contained repo).

test.js:

const { Worker } = require("worker_threads");

if (typeof describe === "undefined") {
  globalThis.describe = globalThis.it = (name, fn) => fn();
  globalThis.expect = () => ({
    toBe() {
      console.log("DONE");
    },
  });
}

describe("test", () => {
  it("test", () => {
    const worker = new Worker(__dirname + "/worker.js");
    worker.unref();

    expect(1).toBe(1);
  });
});

worker.js:

setInterval(() => {
  console.log("XX");
}, 1000);

Expected behavior

When running node test.js it logs "DONE", and the process exits immediately (without logging "XX").

When running test.js with Jest, it (correctly) logs

 PASS  eslint/babel-eslint-parser/test/worker.js
  test
    ✓ test (2 ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        0.588 s, estimated 1 s

and then exits immediately.

When running test.js with Jest and --detectOpenHandles, it logs

Jest has detected the following 1 open handle potentially keeping Jest from exiting:

  ●  WORKER

      15 | describe("test", () => {
      16 |   it("test", () => {
    > 17 |     const worker = new Worker(__dirname + "/helpers/worker.cjs");
         |                    ^
      18 |     worker.unref();
      19 |
      20 |     expect(1).toBe(1);

      at Object.<anonymous> (eslint/babel-eslint-parser/test/worker.js:17:20)
      at TestScheduler.scheduleTests (node_modules/@jest/core/build/TestScheduler.js:347:13)
      at runJest (node_modules/@jest/core/build/runJest.js:387:19)
      at _run10000 (node_modules/@jest/core/build/cli/index.js:408:7)
      at runCLI (node_modules/@jest/core/build/cli/index.js:261:3)

This worker doesn't prevent the process from exiting, so it shouldn't be reported. It should still be reported if you delete worker.unref() from my example.

envinfo

  System:
    OS: Linux 5.11 Ubuntu 21.04 (Hirsute Hippo)
    CPU: (12) x64 Intel(R) Core(TM) i7-8750H CPU @ 2.20GHz
  Binaries:
    Node: 16.3.0 - /usr/local/bin/node
    Yarn: 2.4.1-git.20210125.0f31e6910 - /usr/bin/yarn
    npm: 7.9.0 - ~/.npm-global/bin/npm
  npmPackages:
    jest: ^27.0.0 => 27.0.1 

Context

In the Babel repo we have a test where 90% of the times every test passes, but then Jest waits without ever exiting (and CircleCI kills it after 10 mins without output, marking it as failed). I tried using the --detectOpenHandles option, but it only reports a worker for which I was calling worker.unref() (CircleCI output).

[SimenB]

There is no hasRef for workers, might need node to add support first?

[SimenB]

Filed nodejs/node#42091

[SimenB]

@nicolo-ribaudo fixed in Jest 28.0, but you need node 18.1 which got released an hour ago for the fix that landed in jest 28 to work 😅

[github-actions]

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