components/metrics: Add runtime memory leak detector

components/metrics/leak_detector/call_stack_table.cc

+// 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.
+
+#include "components/metrics/leak_detector/call_stack_table.h"
+
+#include "components/metrics/leak_detector/call_stack_manager.h"
+
+namespace metrics {
+namespace leak_detector {
+
+namespace {
+
+using ValueType = LeakDetectorValueType;
+
+// Get the top |kRankedListSize| entries.

[jar (doing other things), 2015/11/14 02:58:36]

I don't understand this comment.  Perhaps the comment could read:

We only maintain a list of the top |kRankedListSize| entries.

If that is what this variable is for, perhaps a better variable name might be:

kMaxCountOfSuspciousStacks

[Simon Que, 2015/11/17 00:28:48]

Done.

+const int kRankedListSize = 16;
+
+// Initial number of hash table buckets.

[jar (doing other things), 2015/11/14 02:58:36]

nit: your choice... but the name of the variable seems clear... and this comment
then seems redundant (unless you wanted to add some subtlety).

[Simon Que, 2015/11/17 00:28:48]

Done.

+const int kInitialHashTableSize = 1999;
+
+}  // namespace
+
+size_t CallStackTable::StoredHash::operator() (
+    const CallStack* call_stack) const {
+  // The call stack object should already have a hash computed when it was
+  // created.
+  //
+  // This is NOT the actual hash computation function for a new call stack.
+  return call_stack->hash;
+}
+
+CallStackTable::CallStackTable(int call_stack_suspicion_threshold)
+    : num_allocs_(0),
+      num_frees_(0),
+      entry_map_(kInitialHashTableSize),
+      leak_analyzer_(kRankedListSize, call_stack_suspicion_threshold) {
+}
+
+CallStackTable::~CallStackTable() {}
+
+void CallStackTable::Add(const CallStack* call_stack) {
+  auto iter = entry_map_.find(call_stack);
+  Entry* entry = nullptr;
+  if (iter == entry_map_.end()) {
+    entry = &entry_map_[call_stack];

[jar (doing other things), 2015/11/14 02:58:36]

Would it have been enough to just do this operator[]?  Doesn't it work in both
cases (whether find succeeded or failed, inducing the insertion)?

[Simon Que, 2015/11/17 00:28:48]

Done.

+  } else {
+    entry = &iter->second;
+  }
+
+  ++entry->net_num_allocs;
+  ++num_allocs_;
+}
+
+void CallStackTable::Remove(const CallStack* call_stack) {
+  auto iter = entry_map_.find(call_stack);
+  if (iter == entry_map_.end())
+    return;
+  Entry* entry = &iter->second;
+  --entry->net_num_allocs;
+  ++num_frees_;
+
+  // Delete zero-alloc entries to free up space.
+  if (entry->net_num_allocs == 0)
+    entry_map_.erase(iter);
+}
+
+void CallStackTable::TestForLeaks() {
+  // Add all entries to the ranked list.
+  RankedList ranked_list(kRankedListSize);
+
+  for (const auto& entry_pair : entry_map_) {
+    const Entry& entry = entry_pair.second;
+    if (entry.net_num_allocs > 0) {

[jar (doing other things), 2015/11/14 02:58:36]

Given line 65, which seems to discard any entries with net_num_allocs==0, when
is this condition false?

[Simon Que, 2015/11/17 00:28:48]

Done.

+      LeakDetectorValueType call_stack_value(entry_pair.first);
+      ranked_list.Add(call_stack_value, entry.net_num_allocs);
+    }
+  }
+  leak_analyzer_.AddSample(ranked_list.Pass());
+}
+
+}  // namespace leak_detector
+}  // namespace metrics