Fix missing concurrency check in [].forEach.

runtime/lib/growable_array.dart

 // Copyright (c) 2012, 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.
 
 class _GrowableObjectArray<T> implements List<T> {
   factory _GrowableObjectArray._uninstantiable() {
     throw new UnsupportedError(
         "GrowableObjectArray can only be allocated by the VM");
   }
 
@@ skipping 220 matching lines @@
     _setData(new_data);
   }
 
   // Collection interface.
 
   bool contains(T element) {
     return IterableMixinWorkaround.contains(this, element);
   }
 
   void forEach(f(T element)) {
-    // TODO(srdjan): Use IterableMixinWorkaround.forEach(this, f);
-    // Accessing the list directly improves DeltaBlue performance by 25%.
+    int initialLength = length;
     for (int i = 0; i < length; i++) {
       f(this[i]);
+      if (length != initialLength) throw new ConcurrentModificationError(this);

[hausner, 2013/04/25 23:07:17]

This is not sufficient to detect modifications. The mutator could remove one
element and add one. That would go undetected with this check.

I think you need a counter in the array that gets incremented each time the list
is modified. Whether it is worth paying the price for detecting this is another
question.

[Ivan Posva, 2013/04/26 05:58:22]

I think the only concern is that length could change. Basically if you asked for
the length of this List, you'd expect that forEach is called the same number of
times.

     }
   }
 
   String join([String separator = ""]) {
     if (isEmpty) return "";
     if (this.length == 1) return "${this[0]}";
     StringBuffer buffer = new StringBuffer();
     if (separator.isEmpty) {
       for (int i = 0; i < this.length; i++) {
         buffer.write("${this[i]}");
@@ skipping 95 matching lines @@
   }
 
   Set<T> toSet() {
     return new Set<T>.from(this);
   }
 
   Map<int, T> asMap() {
     return IterableMixinWorkaround.asMapList(this);
   }
 }