Adds the ability for ObserverList to not notify observers added during...

base/observer_list.h

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_OBSERVER_LIST_H__
 #define BASE_OBSERVER_LIST_H__
 
+#include <algorithm>
+#include <limits>
 #include <vector>
-#include <algorithm>
 
 #include "base/basictypes.h"
 #include "base/logging.h"
 
 ///////////////////////////////////////////////////////////////////////////////
 //
 // OVERVIEW:
 //
 //   A container for a list of observers.  Unlike a normal STL vector or list,
 //   this container can be modified during iteration without invalidating the
@@ skipping 25 matching lines @@
 //     }
 //
 //     void NotifyBar(int x, int y) {
 //       FOR_EACH_OBSERVER(Observer, observer_list_, OnBar(this, x, y));
 //     }
 //
 //    private:
 //     ObserverList<Observer> observer_list_;
 //   };
 //
+//
 ///////////////////////////////////////////////////////////////////////////////
 
 template <class ObserverType, bool check_empty = false>
 class ObserverList {
  public:
-  ObserverList() : notify_depth_(0) {}
+  // Enumeration of which observers are notified.
+  enum NotificationType {
+    // Specifies that any observers added during notification are notified.
+    // This is the default type if non type is provided to the constructor.
+    NOTIFY_ALL,
+
+    // Specifies that observers added while sending out notification are not
+    // notified.
+    NOTIFY_EXISTING_ONLY
+  };  

[darin (slow to review), 2008/10/30 20:12:50]

nit: add a newline below here.

+  ObserverList() : notify_depth_(0), type_(NOTIFY_ALL) {}
+  ObserverList(NotificationType type) : notify_depth_(0), type_(type) {}
   ~ObserverList() {
     // When check_empty is true, assert that the list is empty on destruction.
     if (check_empty) {
       Compact();
       DCHECK_EQ(observers_.size(), 0U);
     }
   }
 
   // Add an observer to the list.
   void AddObserver(ObserverType* obs) {
@@ skipping 20 matching lines @@
   }
 
   ObserverType* GetElementAt(int index) const {
     return observers_[index];
   }
 
   // An iterator class that can be used to access the list of observers.  See
   // also the FOREACH_OBSERVER macro defined below.
   class Iterator {
    public:
-    Iterator(const ObserverList<ObserverType>& list) : list_(list), index_(0) {
+    Iterator(const ObserverList<ObserverType>& list)
+        : list_(list),
+          index_(0),
+          max_index_(list.type_ == NOTIFY_ALL ?
+                     std::numeric_limits<size_t>::max() :
+                     list.observers_.size()) {
       ++list_.notify_depth_;
     }
 
     ~Iterator() {
       if (--list_.notify_depth_ == 0)
         list_.Compact();
     }
 
     ObserverType* GetNext() {
       ListType& observers = list_.observers_;
       // Advance if the current element is null
-      while (index_ < observers.size() && !observers[index_])
+      size_t max_index = std::min(max_index_, observers.size());
+      while (index_ < max_index && !observers[index_])
         ++index_;
-      return index_ < observers.size() ? observers[index_++] : NULL;
+      return index_ < max_index ? observers[index_++] : NULL;
     }
 
    private:
     const ObserverList<ObserverType>& list_;
     size_t index_;
+    size_t max_index_;
   };
 
  private:
   typedef std::vector<ObserverType*> ListType;
 
   void Compact() const {
     typename ListType::iterator it = observers_.begin();
     while (it != observers_.end()) {
       if (*it) {
         ++it;
       } else {
         it = observers_.erase(it);
       }
     }
   }
 
   // These are marked mutable to facilitate having NotifyAll be const.
   mutable ListType observers_;
   mutable int notify_depth_;
+  NotificationType type_;
 
   friend class ObserverList::Iterator;
 
   DISALLOW_EVIL_CONSTRUCTORS(ObserverList);
 };
 
 #define FOR_EACH_OBSERVER(ObserverType, observer_list, func)  \
   do {                                                        \
     ObserverList<ObserverType>::Iterator it(observer_list);   \
     ObserverType* obs;                                        \
     while ((obs = it.GetNext()) != NULL)                      \
       obs->func;                                              \
   } while (0)
 
 #endif  // BASE_OBSERVER_LIST_H__