[Turbopack] await shutdown before ending pool

packages/next/src/build/turbopack-build/impl.ts

@@ -304,6 +304,7 @@ export async function turbopackBuild(): Promise<{
   }
 }
 
+let shutdownPromise: Promise<void> | undefined
 export async function workerMain(workerData: {
   buildContext: typeof NextBuildContext
 }): Promise<Awaited<ReturnType<typeof turbopackBuild>>> {
@@ -330,5 +331,12 @@ export async function workerMain(workerData: {
   setGlobal('telemetry', telemetry)
 
   const result = await turbopackBuild()
+  shutdownPromise = result.shutdownPromise
   return result
 }
+
+export async function waitForShutdown(): Promise<void> {
+  if (shutdownPromise) {
+    await shutdownPromise
+  }
+}

packages/next/src/build/turbopack-build/index.ts

@@ -11,7 +11,7 @@ async function turbopackBuildWithWorker() {
 
   try {
     const worker = new Worker(path.join(__dirname, 'impl.js'), {
-      exposedMethods: ['workerMain'],
+      exposedMethods: ['workerMain', 'waitForShutdown'],
       numWorkers: 1,
       maxRetries: 0,
       forkOptions: {
@@ -27,8 +27,11 @@ async function turbopackBuildWithWorker() {
       buildContext: prunedBuildContext,
     })
 
-    // destroy worker so it's not sticking around using memory
-    await worker.end()
+    // destroy worker when Turbopack has shutdown so it's not sticking around using memory
+    // We need to wait for shutdown to make sure persistent cache is flushed
+    result.shutdownPromise = worker.waitForShutdown().then(() => {
+      worker.end()
+    })
 
     return result
   } catch (err: any) {