Multi reader/writer cache/buffer

media/blink/rangemap.h

+// Copyright 2015 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 MEDIA_BLINK_RANGEMAP_H_
+#define MEDIA_BLINK_RANGEMAP_H_
+
+#include <map>
+
+#include "base/logging.h"
+
+namespace media {
+
+template<typename KeyType, typename ValueType>
+class RangeMap {
+ public:
+  typedef std::map<KeyType, ValueType> MapType;
+
+  ValueType operator[](KeyType k) const {
+    typename MapType::const_iterator i = map_.upper_bound(k);
+    if (i == map_.begin()) {
+      return 0;
+    } else {
+      --i;
+      return i->second;
+    }
+  }
+
+  // Increase [from..to) by howmuch.
+  void IncrementRange(KeyType from, KeyType to, ValueType howmuch) {
+    DCHECK_GE(to, from);
+    if (from == to || howmuch == 0) return;
+    typename MapType::iterator a = MakeEntry(from);
+    typename MapType::iterator b = MakeEntry(to);
+    for (typename MapType::iterator i = a; i != b; ++i) {
+      i->second += howmuch;
+    }
+    RemoveDuplicates(a);
+    // b may be invalid
+    RemoveDuplicates(map_.lower_bound(to));
+  }
+
+  const MapType& map() { return map_; }
+
+ private:
+  typename MapType::iterator MakeEntry(KeyType k) {
+    typename MapType::value_type tmp(k, 0);
+    std::pair<typename MapType::iterator, bool> insert_result;
+    insert_result = map_.insert(tmp);
+    if (insert_result.second) {
+      if (insert_result.first != map_.begin()) {
+        typename MapType::iterator i = insert_result.first;
+        --i;
+        insert_result.first->second = i->second;
+      }
+    }
+    return insert_result.first;
+  }
+
+  void RemoveDuplicates(typename MapType::iterator i) {
+    if (i == map_.end()) return;
+    if (i == map_.begin() && i->second == 0)  {
+      typename MapType::iterator j = i;
+      ++i;
+      map_.erase(j);
+      if (i == map_.end()) return;
+    }
+    if (i != map_.begin()) {
+      typename MapType::iterator j = i;
+      --i;
+      if (i ->second == j->second) {
+        map_.erase(j);
+      }
+    }
+    typename MapType::iterator j = i;
+    ++j;
+    if (j != map_.end() && i ->second == j->second) {
+      map_.erase(j);
+    }
+  }
+
+  MapType map_;
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BLINK_RANGEMAP_H_