components/metrics: Add runtime memory leak detector

components/metrics/leak_detector/leak_analyzer.h

Index: components/metrics/leak_detector/leak_analyzer.h
diff --git a/components/metrics/leak_detector/leak_analyzer.h b/components/metrics/leak_detector/leak_analyzer.h
new file mode 100644
index 0000000000000000000000000000000000000000..74b674f20e5a75082ffdb1f155d3900e90a9a14f
--- /dev/null
+++ b/components/metrics/leak_detector/leak_analyzer.h
@@ -0,0 +1,97 @@
+// 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 COMPONENTS_METRICS_LEAK_DETECTOR_LEAK_ANALYZER_H_
+#define COMPONENTS_METRICS_LEAK_DETECTOR_LEAK_ANALYZER_H_
+
+#include <map>
+#include <vector>
+
+#include "components/metrics/leak_detector/leak_detector_value_type.h"
+#include "components/metrics/leak_detector/ranked_list.h"
+#include <gperftools/custom_allocator.h>
+
+// This class looks for possible leak patterns in allocation data over time.
+
+namespace leak_detector {
+
+class LeakAnalyzer {
+ public:
+  using ValueType = LeakDetectorValueType;
+
+  template <typename Type>
+  using Allocator = STL_Allocator<Type, CustomAllocator>;
+
+  LeakAnalyzer(uint32_t ranking_size, uint32_t num_suspicions_threshold)
+      : ranking_size_(ranking_size),
+        score_increase_(1 << num_suspicions_threshold),
+        score_threshold_((1 << num_suspicions_threshold) * 2 - 1),

[jar (doing other things), 2015/08/21 02:48:42]

Is it worth a CHECK_LT(num_suspicions_threshold, 30u) in the body, to be sure
these are all as expected (no overflow)?

[Simon Que, 2015/08/21 21:59:20]

I simplified the score system. Now it goes linearly instead of exponentially.

+        ranked_entries_(ranking_size),
+        prev_ranked_entries_(ranking_size) {
+    suspected_leaks_.reserve(ranking_size);
+  }
+
+  ~LeakAnalyzer() {}
+
+  // Take in a list of allocations, sorted by count.
+  void AddSample(const RankedList& ranked_list);
+
+  // Used to report suspected leaks.
+  const std::vector<ValueType, Allocator<ValueType>>& suspected_leaks() const {
+    return suspected_leaks_;
+  }
+
+  // Log the leak detector's top sizes and suspected sizes. Writes output to log
+  // buffer |buffer| of size |size|. Returns the number of bytes remaining in
+  // the buffer after writing to it. The number of bytes remaining includes the
+  // zero terminator that was just written, so this will always return at least
+  // 1, unless |size| == 0.
+  int Dump(char* buffer, const int buffer_size) const;

[jar (doing other things), 2015/08/21 02:48:42]

nit: mutable operands (like buffer), used to convey return values, should come
last.

[Simon Que, 2015/08/21 21:59:20]

Done.

+
+ private:
+  using RankedEntry = RankedList::Entry;
+
+  // Analyze a list of allocation count deltas from the previous iteration. If
+  // anything looks like a possible leak, update the suspicion scores.
+  void AnalyzeDeltas(const RankedList& ranked_deltas);
+
+  // Returns the count for the given value from the previous analysis in
+  // |count|. Returns true if the given value was present in the previous
+  // analysis, or false if not.
+  bool GetPreviousCountForValue(const ValueType& value, uint32_t* count) const;
+
+  // Look for the top |ranking_size_| entries when analyzing leaks.
+  const uint32_t ranking_size_;
+
+  // Each time an entry is suspected as a possible leak, increase its suspicion
+  // score by this much.
+  const uint32_t score_increase_;
+
+  // Report suspected leaks when the suspicion score reaches this value.
+  const uint32_t score_threshold_;
+
+  // A mapping of allocation values to suspicion score. All allocations in this
+  // container are suspected leaks. The score can increase or decrease over
+  // time. Once the score  reaches |score_threshold_|, the entry is reported as
+  // a suspected leak in |suspected_leaks_|.
+  std::map<ValueType,
+           uint32_t,
+           std::less<ValueType>,
+           Allocator<std::pair<ValueType, uint32_t>>> suspected_histogram_;
+
+  // Array of allocated values that passed the suspicion threshold and are being
+  // reported.
+  std::vector<ValueType, Allocator<ValueType>> suspected_leaks_;
+
+  // The most recent allocation entries, since the last call to AddSample().
+  RankedList ranked_entries_;
+  // The previous allocation entries, from before the last call to AddSample().
+  RankedList prev_ranked_entries_;
+
+  DISALLOW_COPY_AND_ASSIGN(LeakAnalyzer);
+};
+
+}  // namespace leak_detector
+
+#endif  // COMPONENTS_METRICS_LEAK_DETECTOR_LEAK_ANALYZER_H_