Allow dev server to exit cleanly (SIGINT/SIGTERM)

Previously we were sending SIGKILL immediately to the child. This
ensures that the child exits as quickly as possible, but it also means
that the child probably won't have time to finish flushing files to
disk (trace files, cache hit statistics, etc.), and can lead to
incomplete writes.

We should give the child a small amount of time to exit cleanly with
SIGINT/SIGTERM before sending SIGKILL. The timeout is needed in case the
child process is unresponsive/hanging.

packages/next/src/cli/next-dev.ts

@@ -35,6 +35,7 @@ import {
 } from '../lib/helpers/get-reserved-port'
 import os from 'os'
 import { once } from 'node:events'
+import { clearTimeout } from 'timers'
 
 type NextDevOptions = {
   turbo?: boolean
@@ -57,13 +58,26 @@ let traceUploadUrl: string
 let sessionStopHandled = false
 let sessionStarted = Date.now()
 
+// How long should we wait for the child to cleanly exit after sending
+// SIGINT/SIGTERM to the child process before sending SIGKILL?
+const CHILD_EXIT_TIMEOUT_MS = 1000
+
 const handleSessionStop = async (signal: NodeJS.Signals | number | null) => {
-  if (child?.pid) child.kill(signal ?? 0)
+  if (signal != null && child?.pid) child.kill(signal)
   if (sessionStopHandled) return
   sessionStopHandled = true
 
-  if (child?.pid && child.exitCode === null && child.signalCode === null) {
+  if (
+    signal != null &&
+    child?.pid &&
+    child.exitCode === null &&
+    child.signalCode === null
+  ) {
+    let exitTimeout = setTimeout(() => {
+      child?.kill('SIGKILL')
+    }, CHILD_EXIT_TIMEOUT_MS)
     await once(child, 'exit').catch(() => {})
+    clearTimeout(exitTimeout)
   }
 
   try {
@@ -124,8 +138,8 @@ const handleSessionStop = async (signal: NodeJS.Signals | number | null) => {
   process.exit(0)
 }
 
-process.on('SIGINT', () => handleSessionStop('SIGKILL'))
-process.on('SIGTERM', () => handleSessionStop('SIGKILL'))
+process.on('SIGINT', () => handleSessionStop('SIGINT'))
+process.on('SIGTERM', () => handleSessionStop('SIGTERM'))
 
 // exit event must be synchronous
 process.on('exit', () => child?.kill('SIGKILL'))
@@ -291,7 +305,9 @@ const nextDev = async (
           }
           return startServer(startServerOptions)
         }
-        await handleSessionStop(signal)
+        // Call handler (e.g. upload telemetry). Don't try to send a signal to
+        // the child, as it has already exited.
+        await handleSessionStop(/* signal */ null)
       })
     })
   }