cc: Adding BeginFrameObserverMap.

cc/scheduler/begin_frame_observer_map.h

Index: cc/scheduler/begin_frame_observer_map.h
diff --git a/cc/scheduler/begin_frame_observer_map.h b/cc/scheduler/begin_frame_observer_map.h
new file mode 100644
index 0000000000000000000000000000000000000000..006403074b6b4003e4938d0c9ed08001d1ef2f11
--- /dev/null
+++ b/cc/scheduler/begin_frame_observer_map.h
@@ -0,0 +1,157 @@
+// Copyright 2014 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 CC_SCHEDULER_BEGIN_FRAME_OBSERVER_MAP_H_
+#define CC_SCHEDULER_BEGIN_FRAME_OBSERVER_MAP_H_
+
+#include "base/containers/hash_tables.h"
+#include "base/logging.h"
+
+namespace cc {
+
+template <class ObserverType, class ObserverDataType>
+class BeginFrameObserverMap {
+ private:
+  typedef typename base::hash_set<ObserverType*> SetType;
+  typedef typename base::hash_map<ObserverType*, ObserverDataType*> MapType;
+
+  MapType observers_;
+
+  volatile size_t const_iterators_;
+  size_t iterators_;
+  MapType observers_to_add_;
+  SetType observers_to_remove_;
+
+ public:
+  BeginFrameObserverMap()
+      : observers_(),
+        const_iterators_(0),
+        iterators_(0),
+        observers_to_add_(),
+        observers_to_remove_() {}
+
+  class iterator : public MapType::iterator {
+   public:
+    explicit iterator(
+        typename MapType::iterator it,
+        BeginFrameObserverMap<ObserverType, ObserverDataType>* list)
+        : MapType::iterator(it), list_(list) {
+      list_->iterators_++;
+    }
+    ~iterator() {
+      DCHECK_GT(list_->iterators_, 0U);
+      list_->iterators_--;
+      list_->CompactMaps();
+    }
+
+   private:
+    BeginFrameObserverMap<ObserverType, ObserverDataType>* list_;
+  };
+
+  class const_iterator : public MapType::const_iterator {
+   public:
+    explicit const_iterator(
+        typename MapType::const_iterator it,
+        const BeginFrameObserverMap<ObserverType, ObserverDataType>* list)
+        : MapType::const_iterator(it),
+          list_(const_cast<
+                BeginFrameObserverMap<ObserverType, ObserverDataType>*>(list)) {
+      list_->const_iterators_++;
+    }
+    ~const_iterator() {
+      DCHECK_GT(list_->const_iterators_, 0U);
+      list_->const_iterators_--;
+    }
+
+   private:
+    BeginFrameObserverMap<ObserverType, ObserverDataType>* list_;
+  };
+
+  void AddObserver(ObserverType* obs) {
+    DCHECK_EQ(const_iterators_, 0U);
+    if (observers_to_add_.count(obs) == 0) {
+      observers_to_add_[obs] = new ObserverDataType();
+    }
+    CompactMaps();
+  }
+
+  void RemoveObserver(ObserverType* obs) {
+    DCHECK_EQ(const_iterators_, 0U);
+    observers_to_remove_.insert(obs);
+    CompactMaps();
+  }
+
+  bool HasObservers() const { return !observers_.empty(); }
+  bool HasObserver(ObserverType* const obs) const {
+    return (*this)[obs] != nullptr;
+  }
+
+  iterator begin() { return iterator(observers_.begin(), this); }
+  iterator end() { return iterator(observers_.end(), this); }
+
+  const_iterator cbegin() const {
+    return const_iterator(const_cast<const MapType*>(&observers_)->begin(),
+                          this);
+  }
+
+  const_iterator cend() const {
+    return const_iterator(const_cast<const MapType*>(&observers_)->end(), this);
+  }
+
+  const_iterator begin() const { return cbegin(); }
+  const_iterator end() const { return cend(); }
+
+  ObserverDataType* operator[](ObserverType* const obs) {
+    {
+      auto it = observers_.find(obs);
+      if (it != observers_.end())
+        return it->second;
+    }
+    {
+      auto it = observers_to_add_.find(obs);
+      if (it != observers_to_add_.end())
+        return it->second;
+    }
+    return nullptr;
+  }
+  const ObserverDataType* operator[](ObserverType* const obs) const {
+    {
+      auto it = observers_.find(obs);
+      if (it != observers_.end())
+        return it->second;
+    }
+    {
+      auto it = observers_to_add_.find(obs);
+      if (it != observers_to_add_.end())
+        return it->second;
+    }
+    return nullptr;
+  }
+
+ private:
+  void CompactMaps() {
+    if (iterators_ != 0)
+      return;
+
+    for (auto it = observers_to_remove_.begin();
+         it != observers_to_remove_.end(); it++) {
+      delete observers_[*it];
+      observers_[*it] = nullptr;
+      observers_.erase(*it);
+    }
+    observers_to_remove_.clear();
+
+    for (auto it = observers_to_add_.begin(); it != observers_to_add_.end();
+         it++) {
+      observers_[it->first] = it->second;
+    }
+    observers_to_add_.clear();
+  }
+
+  friend class BeginFrameObserverMapTest;
+};
+
+}  // namespace cc
+
+#endif  // CC_SCHEDULER_BEGIN_FRAME_OBSERVER_MAP_H_