perf(dev): print Ready early and defer initialization #87942
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This was referenced Dec 30, 2025
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Comment on lines
+376
to
+389
| // Print "Ready" immediately for fast perceived startup | ||
| // Requests will wait via handlersPromise until init completes | ||
| const startServerProcessDuration = | ||
| performance.mark('next-start-end') && | ||
| performance.measure( | ||
| 'next-start-duration', | ||
| 'next-start', | ||
| 'next-start-end' | ||
| ).duration | ||
| const formatDurationText = | ||
| startServerProcessDuration > 2000 | ||
| ? `${Math.round(startServerProcessDuration / 100) / 10}s` | ||
| : `${Math.round(startServerProcessDuration)}ms` | ||
| Log.event(`Ready in ${formatDurationText}`) |
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The "Ready in Xms" message is printed before the heavy initialization completes. If initialization fails (at line 457-469), the misleading "Ready" message has already been logged, but the server exits with an error.
View Details
📝 Patch Details
diff --git a/packages/next/src/server/lib/start-server.ts b/packages/next/src/server/lib/start-server.ts
index ea219758a9..169b46a716 100644
--- a/packages/next/src/server/lib/start-server.ts
+++ b/packages/next/src/server/lib/start-server.ts
@@ -373,21 +373,6 @@ export async function startServer(
logBundler: isDev,
})
- // Print "Ready" immediately for fast perceived startup
- // Requests will wait via handlersPromise until init completes
- const startServerProcessDuration =
- performance.mark('next-start-end') &&
- performance.measure(
- 'next-start-duration',
- 'next-start',
- 'next-start-end'
- ).duration
- const formatDurationText =
- startServerProcessDuration > 2000
- ? `${Math.round(startServerProcessDuration / 100) / 10}s`
- : `${Math.round(startServerProcessDuration)}ms`
- Log.event(`Ready in ${formatDurationText}`)
-
let cleanupStarted = false
let closeUpgraded: (() => void) | null = null
const cleanup = () => {
@@ -474,6 +459,20 @@ export async function startServer(
handlersReady()
+ // Print "Ready" only after successful initialization
+ const startServerProcessDuration =
+ performance.mark('next-start-end') &&
+ performance.measure(
+ 'next-start-duration',
+ 'next-start',
+ 'next-start-end'
+ ).duration
+ const formatDurationText =
+ startServerProcessDuration > 2000
+ ? `${Math.round(startServerProcessDuration / 100) / 10}s`
+ : `${Math.round(startServerProcessDuration)}ms`
+ Log.event(`Ready in ${formatDurationText}`)
+
if (process.env.TURBOPACK && isDev) {
await validateTurboNextConfig({
dir: serverOptions.dir,
Analysis
Misleading "Ready in Xms" message logged before critical initialization completes
What fails: Server prints "Ready in Xms" message at line 389 before calling getRequestHandlers() at line 457. If initialization fails, the "Ready" message has already been logged to the user's console, but then the server exits with an error.
How to reproduce:
- Create a configuration scenario that causes
getRequestHandlers()to throw an error (e.g., corrupted config, missing dependencies during initialization) - Start the Next.js dev server
- Observe that "Ready in Xms" is logged to console
- The server then exits with an error code and prints the error stack trace
Result: Users see misleading output suggesting the server started successfully when it actually failed during initialization.
Expected: The "Ready" message should only be logged after getRequestHandlers() completes successfully. If initialization fails, the "Ready" message should never be printed.
Root cause: Commit 3e57cf5 ("perf(dev): print Ready early and defer initialization") moved the "Ready" log message before the critical getRequestHandlers() initialization call as a performance optimization. While the defensive mechanism via handlersPromise prevents request processing until initialization completes, it does not prevent the misleading log message from being printed on failure.
Fix: Moved the "Ready in Xms" log message to after handlersReady() is called (line 461-475), ensuring it only prints after successful initialization. The log now correctly appears after all critical initialization in getRequestHandlers() completes.
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- Print "Ready in Xms" immediately when HTTP server starts listening - Defer heavy initialization (config, bundler, etc.) to background - First request waits for init via existing handlersPromise mechanism - Fix shell script symlink resolution for pnpm node_modules/.bin - Fix Rust CLI canonicalize for symlink resolution - Extract getSupportedBrowsers to lightweight module This reduces perceived startup time from ~300ms to ~50-100ms. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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❌ 7 failing tests in 3 jobs⏳ CI running (3 jobs reported) · Updated 2026-01-01 20:54:44 UTC · Commit: 79adf32
Details📁
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❌ 121 failing tests in 3 jobs⏳ CI running (3 jobs reported) · Updated 2026-01-01 21:01:15 UTC · Commit: 79adf32
Details📁
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CodSpeed Performance ReportMerging #87942 will not alter performanceComparing Summary
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Summary
Benchmark Results (cumulative - final)
Total Improvement (Canary → Final)
Test Plan
🤖 Generated with Claude Code