components/metrics: Add runtime memory leak detector

third_party/tcmalloc/chromium/src/ranked_list.h

+// Copyright (c) 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.
+
+// ---
+// Author: Simon Que
+
+#ifndef _RANKED_LIST_H_
+#define _RANKED_LIST_H_
+
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/custom_allocator.h"
+#include "base/stl_allocator.h"
+
+// RankedList lets you add entries and automatically sorts them internally, so
+// they can be accessed in sorted order. The entries are stored as a vector
+// array.
+
+namespace leak_detector {
+
+template <typename T>
+class RankedList {
+ public:
+  // A single entry in the RankedList. The RankedList sorts entries by |count|.
+  struct Entry {
+    int count;
+    T value;
+  };
+
+  RankedList(size_t max_size) : max_size_(max_size) {
+    entries_.reserve(max_size + 1);
+  }
+  ~RankedList() {}
+
+  // Access individual element. Does not do boundary checking.
+  const Entry& entry(int index) const {
+    return entries_[index];
+  }
+  size_t size() const {
+    return entries_.size();
+  }
+
+  // Add a new value-count pair to the list. Does not check for existing entries
+  // with the same value.
+  void Add(const T& value, int count);
+
+ private:
+  // Returns the position to insert a new value. Returns -1 if it cannot be
+  // inserted.
+  int GetInsertionIndex(int count) const;
+
+  // Max and min counts.
+  const int max_count() const {
+    return entries_.empty() ? 0 : entries_[0].count;
+  }
+  const int min_count() const {
+    return entries_.empty() ? 0 : entries_[size() - 1].count;
+  }
+
+  // Max number of items in the list.
+  size_t max_size_;
+
+  // Points to the array of entries.
+  std::vector<Entry, STL_Allocator<Entry, CustomAllocator>> entries_;
+};
+
+template <typename T>
+void RankedList<T>::Add(const T& value, int count) {
+  // Determine where to insert the value.
+  int index = GetInsertionIndex(count);
+  if (index == -1)
+    return;
+
+  entries_.emplace(entries_.begin() + index, Entry({count, value}));
+
+  // Limit the list size if it exceeds the maximum allowed size.
+  if (entries_.size() > max_size_)
+    entries_.resize(max_size_);
+}
+
+template <typename T>
+int RankedList<T>::GetInsertionIndex(int count) const {

[jar (doing other things), 2015/07/20 22:19:03]

I'm again a bit surprised to see larger code blocks (even templated) in headers.
 Is this perf critical code... used in very few places... so inlining is needed?

+  // If the list is full, do not add any entry with |count| if does not exceed
+  // the lowest count of the entries in the list.
+  if (size() == max_size_ && count <= min_count())
+    return -1;
+  // If larger than the current largest item, insert it before.
+  if (count >= max_count())
+    return 0;
+  // If smaller than the current smallest item, but the list is not full,
+  // insert it after.
+  if (count <= min_count())
+    return size();
+
+    // Otherwise it's somewhere in the middle, so look for it there.
+  int min_pos = 0;
+  int max_pos = size() - 1;
+  while (max_pos >= min_pos) {
+    int midpoint = (max_pos + min_pos) / 2;
+    if (count >= entries_[midpoint].count &&
+        count <= entries_[midpoint - 1].count) {
+      return midpoint;
+    }
+    // The list is reverse sorted.
+    if (entries_[midpoint].count >= count)
+      min_pos = midpoint + 1;
+    else
+      max_pos = midpoint - 1;
+  }
+  return max_pos;
+}
+
+}  // namespace leak_detector
+
+#endif  // _RANKED_LIST_H_