Fix a race condition in file watcher.

lib/src/file_watcher/polling.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library watcher.file_watcher.polling;
 
 import 'dart:async';
 import 'dart:io';
 
 import '../file_watcher.dart';
@@ skipping 33 matching lines @@
   _PollingFileWatcher(this.path, Duration pollingDelay) {
     _timer = new Timer.periodic(pollingDelay, (_) => _poll());
     _poll();
   }
 
   /// Checks the mtime of the file and whether it's been removed.
   Future _poll() async {
     // We don't mark the file as removed if this is the first poll (indicated by
     // [_lastModified] being null). Instead, below we forward the dart:io error
     // that comes from trying to read the mtime below.
-    if (_lastModified != null && !await new File(path).exists()) {
+    var pathExists = await new File(path).exists();
+    if (_eventsController.isClosed) return;
+
+    if (_lastModified != null && !pathExists) {
       _eventsController.add(new WatchEvent(ChangeType.REMOVE, path));
       close();
       return;
     }
 
     var modified;
     try {
-      modified = await getModificationTime(path);
+      try {
+        modified = await getModificationTime(path);
+      } finally {

[Bob Nystrom, 2015/07/17 15:58:22]

Can you just add this to the outer try?

[nweiz, 2015/07/17 20:42:18]

No, it needs to happen before "_eventsController.addError" in the catch block.

+        if (_eventsController.isClosed) return;
+      }
     } on FileSystemException catch (error, stackTrace) {
       _eventsController.addError(error, stackTrace);
       close();
       return;
     }
 
-    if (_eventsController.isClosed) return;
     if (_lastModified == modified) return;
 
     if (_lastModified == null) {
       // If this is the first poll, don't emit an event, just set the last mtime
       // and complete the completer.
       _lastModified = modified;
       _readyCompleter.complete();
     } else {
       _lastModified = modified;
       _eventsController.add(new WatchEvent(ChangeType.MODIFY, path));
     }
   }
 
   void close() {
     _timer.cancel();
     _eventsController.close();
   }
 }