How would you offload a CPU-intensive task using worker threads?

Direct answer

Spawn a worker pool with worker_threads, post job data via workerData/postMessage, return result to main thread, terminate or reuse workers — keep HTTP handler async awaiting worker result without blocking the event loop.

Scenario: hash 10k passwords or parse a huge JSON export without freezing the AceDevHub API for other users (Q68–69, Q74).

Worker file — isolate CPU logic in hash-worker.mjs.
Pool — fixed N workers; queue jobs in main thread.
Timeout — worker.terminate() if job exceeds SLA.
Fallback — BullMQ job for very long tasks instead of inline worker.

scenario-worker-pool.mjs

import { Worker } from "node:worker_threads";

function runCpuJob(payload) {
  return new Promise((resolve, reject) => {
    const worker = new Worker("./cpu-worker.mjs", { workerData: payload });
    const timer = setTimeout(() => {
      worker.terminate();
      reject(new Error("WORKER_TIMEOUT"));
    }, 30_000);

    worker.on("message", (result) => { clearTimeout(timer); resolve(result); });
    worker.on("error", reject);
  });
}

// Route: const hash = await runCpuJob({ password });