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"
+
+namespace leak_detector {
+
+namespace {
+
+using ValueType = LeakDetectorValueType;
+
+// Get the top |kRankedListSize| entries.
+const int kRankedListSize = 16;
+
+// Initial number of hash table buckets.
+const int kInitialHashTableSize = 1999;
+
+// Used for printing call stacks in LeakAnalyzer.
+class StringPrint : public LeakAnalyzer::StringPrint {
+ public:
+  // Gets the string representation of a value.
+  virtual const char* ValueToString(const ValueType& value, bool spacing_on) {
+    const CallStack* call_stack = value.call_stack();
+    snprintf(buffer_, sizeof(buffer_), spacing_on ? "%16p" : "%p", call_stack);
+    return buffer_;
+  }
+
+  // Gets the word that describes the value type.
+  virtual const char* ValueTypeName(bool is_plural) {
+    return is_plural ? "call stacks" : "call stack";
+  }
+} string_print;
+
+}  // namespace
+
+long CallStackTable::Hash::operator() (const CallStack* call_stack) const {
+  // The call stack object should already have a hash computed when it was
+  // created.
+  return call_stack->hash;

[jar (doing other things), 2015/08/15 03:29:01]

Does this give a warning as a hash of type uint64_t is converted to a long?

[Simon Que, 2015/08/15 23:28:30]

No, but this should all be size_t, according to the unordered_map
specifications.

+}
+
+CallStackTable::CallStackTable(int call_stack_suspicion_threshold)
+    : num_allocs_(0),
+      num_frees_(0),
+      entry_map_(kInitialHashTableSize),
+      leak_analyzer_(kRankedListSize, call_stack_suspicion_threshold,
+                     &string_print) {
+}
+
+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];
+  } else {
+    entry = &iter->second;
+  }
+
+  ++entry->num_allocs;
+  ++num_allocs_;
+}
+
+void CallStackTable::Remove(const CallStack* call_stack) {
+  auto iter = entry_map_.find(call_stack);
+  if (iter == entry_map_.end())

[jar (doing other things), 2015/08/15 03:29:01]

Is this an internal error, or a regular occurrence?

[Simon Que, 2015/08/15 23:28:30]

This should not happen unless there was an error elsewhere, e.g:
- A double free.
- Improper sampling of allocs and frees in the leak detector

It's not a regular occurrence but it could happen if there was bad code
elsewhere.

+    return;
+  Entry* entry = &iter->second;
+  ++entry->num_frees;
+  ++num_frees_;
+
+  // If there are no net allocs, delete the entry.
+  if (entry->num_allocs == entry->num_frees)
+    entry_map_.erase(iter);
+}
+
+int CallStackTable::Dump(char* buffer, const int buffer_size) const {
+  int size_left = buffer_size;
+
+  if (entry_map_.empty())
+    return size_left;
+
+  int attempted_size =
+      snprintf(buffer, size_left,
+               "Total number of allocations: %u\n"
+                   "Total number of frees: %u\n"
+                   "Net number of allocations: %u\n"
+                   "Total number of distinct stack traces: %zu\n",
+               num_allocs_, num_frees_, num_allocs_ - num_frees_,
+               entry_map_.size());
+  size_left -= attempted_size;
+  buffer += attempted_size;
+
+  if (size_left > 0) {

[jar (doing other things), 2015/08/15 03:29:01]

Please correct this throughout this CL.

This should probably be a test for > 1.  Size left should never be zero.

[Simon Que, 2015/08/15 23:28:30]

Done.

+    int attempted_size = leak_analyzer_.Dump(buffer, size_left);
+    size_left -= attempted_size;
+    buffer += attempted_size;
+  }
+
+  if (size_left > 0)

[jar (doing other things), 2015/08/15 03:29:01]

This is always true.

[Simon Que, 2015/08/15 23:28:30]

Done.

+    return buffer_size - size_left;
+
+  return buffer_size;
+}
+
+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.num_allocs != entry.num_frees) {
+      LeakDetectorValueType call_stack_value(entry_pair.first);
+      ranked_list.Add(call_stack_value, entry.num_allocs - entry.num_frees);
+    }
+  }
+  leak_analyzer_.AddSample(ranked_list);
+}
+
+}  // namespace leak_detector