Ensure workers are cleaned up always (#71564)

This ensures we properly clean up workers even if an error is thrown
before our normal `.end()` call is done. This can be verified currently
by building `pnpm next test/e2e/app-dir/dynamic-io` which should
encounter an error and fail but the workers were previously being kept
and using lots of CPU, now they are properly cleaned up.

packages/next/src/lib/verifyAndLint.ts

@@ -15,8 +15,14 @@ export async function verifyAndLint(
   enableWorkerThreads: boolean | undefined,
   telemetry: Telemetry
 ): Promise<void> {
+  let lintWorkers:
+    | (Worker & {
+        runLintCheck: typeof import('./eslint/runLintCheck').runLintCheck
+      })
+    | undefined
+
   try {
-    const lintWorkers = new Worker(require.resolve('./eslint/runLintCheck'), {
+    lintWorkers = new Worker(require.resolve('./eslint/runLintCheck'), {
       numWorkers: 1,
       enableWorkerThreads,
       maxRetries: 0,
@@ -37,7 +43,7 @@ export async function verifyAndLint(
       []
     )
 
-    const lintResults = await lintWorkers.runLintCheck(dir, lintDirs, {
+    const lintResults = await lintWorkers?.runLintCheck(dir, lintDirs, {
       lintDuringBuild: true,
       eslintOptions: {
         cacheLocation,
@@ -63,8 +69,6 @@ export async function verifyAndLint(
     if (lintOutput) {
       console.log(lintOutput)
     }
-
-    lintWorkers.end()
   } catch (err) {
     if (isError(err)) {
       if (err.type === 'CompileError' || err instanceof CompileError) {
@@ -77,5 +81,9 @@ export async function verifyAndLint(
       }
     }
     throw err
+  } finally {
+    try {
+      lintWorkers?.end()
+    } catch {}
   }
 }

packages/next/src/lib/worker.ts

@@ -38,6 +38,11 @@ export class Worker {
 
     this._worker = undefined
 
+    // ensure we end workers if they weren't before exit
+    process.on('exit', () => {
+      this.close()
+    })
+
     const createWorker = () => {
       // Get the node options without inspect and also remove the
       // --max-old-space-size flag as it can cause memory issues.