fix: make perf benchmark script more reliable

- Fix lsof() bug: .toString (property ref) -> .toString() (method call)
  and wrap in try/catch for non-zero exit codes
- Replace fixed sleep(5000) + broken lsof check with waitForServer()
  that polls with HTTP fetch until servers actually respond
- Store startVitePreview child processes and add .catch() error handlers

Co-authored-by: NullVoxPopuli <[email protected]>
Agent-Logs-Url: https://github.com/emberjs/ember.js/sessions/abc30b6b-e3d1-44c5-988e-648096650173

Author: Copilot

bin/benchmark/run.mjs

@@ -6,7 +6,7 @@ import fs from 'fs-extra';
 
 import { getOrBuildControlTarball } from './control.mjs';
 import { buildExperimentTarball } from './experiment.mjs';
-import { run, prepareApp, sleep, startVitePreview, lsof } from './utils.mjs';
+import { run, prepareApp, startVitePreview, waitForServer } from './utils.mjs';
 
 const { ensureDir, remove } = fs;
 
@@ -112,12 +112,20 @@ export async function runBenchmark({ force = false, reuse = false, headless = tr
   ]);
 
   // These will error if the parts are occupied (--strict-port)
-  startVitePreview({ appDir: CONTROL_DIRS.app, port: DEFAULT_CONTROL_PORT });
-  startVitePreview({
+  const controlServer = startVitePreview({ appDir: CONTROL_DIRS.app, port: DEFAULT_CONTROL_PORT });
+  const experimentServer = startVitePreview({
     appDir: EXPERIMENT_DIRS.app,
     port: DEFAULT_EXPERIMENT_PORT,
   });
 
+  // Fail fast if either server process exits unexpectedly during startup
+  controlServer.catch((err) => {
+    console.error('Control server exited unexpectedly:', err.message);
+  });
+  experimentServer.catch((err) => {
+    console.error('Experiment server exited unexpectedly:', err.message);
+  });
+
   try {
     await bootAndRun({ headless });
   } finally {
@@ -132,20 +140,13 @@ async function bootAndRun({ headless = true } = {}) {
   const experimentUrl = `http://127.0.0.1:${DEFAULT_EXPERIMENT_PORT}`;
   const markersString = buildMarkersString(DEFAULT_MARKERS);
 
-  // give servers a moment to start
-  await sleep(5000);
-
-  /**
-   * We need to make sure both servers are running before starting the benchmark.
-   */
-  let controlLsof = await lsof(DEFAULT_CONTROL_PORT);
-  let experimentLsof = await lsof(DEFAULT_EXPERIMENT_PORT);
-
-  if (!controlLsof || !experimentLsof) {
-    throw new Error(
-      `One of the servers failed to start. Control server lsof:\n${controlLsof}\n\nExperiment server lsof:\n${experimentLsof}`
-    );
-  }
+  // Wait for both servers to be ready (HTTP-level check with retries)
+  console.log('\n\tWaiting for servers to be ready...');
+  await Promise.all([
+    waitForServer(controlUrl, { timeout: 30_000 }),
+    waitForServer(experimentUrl, { timeout: 30_000 }),
+  ]);
+  console.log('\tBoth servers are ready.\n');
 
   const tracerbenchBin = join(REPO_ROOT, 'node_modules/tracerbench/bin/run');
 

bin/benchmark/utils.mjs

@@ -23,8 +23,38 @@ export function sleep(ms) {
   return new Promise((resolve) => setTimeout(resolve, ms));
 }
 
-export async function lsof(port) {
-  return execSync(`lsof -i :${port} -P -n`).toString;
+export function lsof(port) {
+  try {
+    return execSync(`lsof -i :${port} -P -n`).toString();
+  } catch {
+    return null;
+  }
+}
+
+/**
+ * Wait for a server to respond to HTTP requests.
+ * Polls with fetch until the server returns a response (any status),
+ * retrying on connection errors.
+ *
+ * @param {string} url - The URL to poll
+ * @param {object} [options]
+ * @param {number} [options.timeout=30000] - Max time to wait in ms
+ * @param {number} [options.interval=500] - Time between retries in ms
+ */
+export async function waitForServer(url, { timeout = 30_000, interval = 500 } = {}) {
+  const deadline = Date.now() + timeout;
+
+  while (Date.now() < deadline) {
+    try {
+      await fetch(url);
+      return; // any response means the server is up
+    } catch {
+      // connection refused / not ready yet — wait and retry
+      await sleep(interval);
+    }
+  }
+
+  throw new Error(`Server at ${url} did not respond within ${timeout}ms`);
 }
 
 export async function buildEmberSource(cwd) {