One idea I had was that here we could tell the worker to process.exit if main thread's worker.terminate was taking too long or got stuck.

setTimeout(() => {
  this.worker.postMessage('TERMINATE_NOW')
  reject(new Error('Failed to terminate worker')
})

Worker would catch this:

// worker.ts
parentPort.on('message', (message) => {
  // Main thread tried to terminate this worker but failed, let's force the exit here in worker
  if (message === 'TERMINATE_NOW') {
    process.exit()
  }
})

But it seems that this does not work. The worker never receives the message. I guess the worker.terminate() has already closed the message channel even though it has not yet resolved completely.

can't we just await the terminate instead of using the then keyword? if not, why?

We cannot await as the outer Promise has to be the return value.

This outer Promise is required since setTimeout is used to decide when destroy function should reject. This would not work:

async function destroy() {
  setTimeout(() => {
    throw new Error("Timeout error")
  }, 1000);

  await sleep(2000);
}

destroy().then(() => console.log("success")).catch(() => console.log("Failed"))

> Uncaught Error: Timeout error
> success

Wrapping everything in a outer Promise helps:

async function destroy() {
  let resolve, reject;
  const outerPromise = new Promise((res, rej) => {
    resolve = res
    reject = rej
  })
  
  setTimeout(() => {
    reject(new Error("Timeout error"))
  }, 1000);

  sleep(2000).then(resolve);

  return outerPromise;
}

destroy().then(() => console.log("success")).catch(() => console.log("Failed"))

> Failed

Similar pattern is used in runTask: