node:worker_threads exits too early

[bartlomieju]

Version: Deno 1.41.3

This bug was introduced in #22647.

Consider following script:

// worker.mjs
import { isMainThread, Worker } from "node:worker_threads";

if (isMainThread) {
  // This re-loads the current file inside a Worker instance.
  const w = new Worker(import.meta.filename);
} else {
  console.log("Inside Worker!");
  console.log(isMainThread); // Prints 'false'.
}

$ deno run -A worker.mjs
Inside Worker!
false

$ node worker.mjs
Inside Worker!
false

Consider this script:

// worker.mjs
import { isMainThread, parentPort, Worker } from "node:worker_threads";

if (isMainThread) {
  // This re-loads the current file inside a Worker instance.
  const w = new Worker(import.meta.filename);
} else {
  console.log("Inside Worker!");
  console.log(isMainThread); // Prints 'false'.
  parentPort.on("message", () => console.log("Got message from main thread");
}

$ deno run -A worker.mjs
Inside Worker!
false
# exits

$ node worker.mjs
Inside Worker!
false
# waits indefinitely

And this one:

// worker.mjs
import { isMainThread, parentPort, Worker } from "node:worker_threads";

function onMessageOneshot() {
  console.log("Got message from main thread!");
  parentPort.off("message", onMessageOneshot);
}

if (isMainThread) {
  // This re-loads the current file inside a Worker instance.
  const w = new Worker(import.meta.filename);

  setTimeout(() => {
    w.postMessage("Hello! I am from the main thread.");
  }, 1000);
} else {
  console.log("Inside Worker!");
  console.log(isMainThread); // Prints 'false'.
  parentPort.on("message", onMessageOneshot);
}

$ deno run -A worker.mjs
Inside Worker!
false
# exits

$ node worker.mjs
Inside Worker!
false
# waits 1s
Got message from main thread!
# exits

We need to fix condition for unrefing the op waiting for message inside a worker. We should only unref the op if there are no active message listeners.

Ref #22911