limit open files on macOS when copying assets (#34050)

packages/flutter_tools/lib/src/bundle.dart

@@ -5,6 +5,7 @@
 import 'dart:async';
 
 import 'package:meta/meta.dart';
+import 'package:pool/pool.dart';
 
 import 'artifacts.dart';
 import 'asset.dart';
@@ -226,10 +227,17 @@ Future<void> writeBundle(
     bundleDir.deleteSync(recursive: true);
   bundleDir.createSync(recursive: true);
 
+  // Limit number of open files to avoid running out of file descriptors.
+  final Pool pool = Pool(64);
   await Future.wait<void>(
     assetEntries.entries.map<Future<void>>((MapEntry<String, DevFSContent> entry) async {
-      final File file = fs.file(fs.path.join(bundleDir.path, entry.key));
-      file.parent.createSync(recursive: true);
-      await file.writeAsBytes(await entry.value.contentsAsBytes());
+      final PoolResource resource = await pool.request();
+      try {
+        final File file = fs.file(fs.path.join(bundleDir.path, entry.key));
+        file.parent.createSync(recursive: true);
+        await file.writeAsBytes(await entry.value.contentsAsBytes());
+      } finally {
+        resource.release();
+      }
     }));
 }