[tracing] Introduce support for userland memory allocators dumps.

base/trace_event/memory_allocator_dump.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 "base/trace_event/memory_allocator_dump.h"
+
+#include "base/format_macros.h"
+#include "base/trace_event/memory_allocator_attributes.h"
+#include "base/trace_event/memory_dump_manager.h"
+#include "base/trace_event/memory_dump_provider.h"
+#include "base/trace_event/trace_event_argument.h"
+#include "base/values.h"
+
+namespace base {
+namespace trace_event {
+
+MemoryAllocatorDump::MemoryAllocatorDump(const std::string& name,
+                                         MemoryAllocatorDump* parent)
+    : name_(name),
+      parent_(parent),
+      physical_size_in_bytes_(0),
+      allocated_objects_count_(0),
+      allocated_objects_size_in_bytes_(0) {
+}
+
+MemoryAllocatorDump::~MemoryAllocatorDump() {
+}
+
+void MemoryAllocatorDump::SetExtraAttribute(const std::string& name,
+                                            int value) {
+  extra_attributes_.SetInteger(name, value);
+}
+
+int MemoryAllocatorDump::GetExtraIntegerAttribute(
+    const std::string& name) const {
+  bool res;
+  int value = -1;
+  res = extra_attributes_.GetInteger(name, &value);
+  DCHECK(res) << "Allocator attribute '" << name << "' not found";
+  return value;
+}
+
+void MemoryAllocatorDump::AsValueInto(TracedValue* value) const {
+  value->BeginDictionary(name_.c_str());
+
+  value->SetString("parent", parent_ ? parent_->name_ : "");
+  value->SetInteger("physical_size", physical_size_in_bytes_);
+  value->SetInteger("allocated_objects_count", allocated_objects_count_);
+  value->SetInteger("allocated_objects_size", allocated_objects_size_in_bytes_);
+
+  // Copy all the extra attributes.
+  const MemoryDumpProvider* mdp =
+      MemoryDumpManager::GetInstance()->dump_provider_currently_active();
+  const MemoryAllocatorDeclaredAttributes& extra_attributes_types =
+      mdp->allocator_attributes();

[picksi, 2015/03/16 09:18:06]

mdp can bull a nullptr if this is called when a dump isn't going on. Should you
DCHECK this?

[Primiano Tucci (use gerrit), 2015/03/16 09:57:17]

Usually the rule in chromium is to NOT dcheck for null pointer dereference.
Rationale: if you deref a null ptr, you will get a segfault and the stack trace
will point at that line. DCHECK is not going to add any extra useful behavior,
and just add more code clutter.
It would be different, though, if you want to doublecheck some consistency
(e.g., "If I am in state A, I expect this pointer, which I am not using here, to
be null or non-null"), but this is not the case here.

+
+  value->BeginDictionary("args");
+  for (DictionaryValue::Iterator it(extra_attributes_); !it.IsAtEnd();
+       it.Advance()) {
+    const std::string& attr_name = it.key();
+    const Value& attr_value = it.value();
+    value->BeginDictionary(attr_name.c_str());
+    value->SetValue("value", attr_value.DeepCopy());
+
+    auto attr_it = extra_attributes_types.find(attr_name);
+    DCHECK(attr_it != extra_attributes_types.end())
+        << "Allocator attribute " << attr_name
+        << " not declared for the dumper " << mdp->GetFriendlyName();
+    value->SetString("type", attr_it->second.type);
+
+    value->EndDictionary();  // "arg_name": { "type": "...", "value": "..." }
+  }
+  value->EndDictionary();  // "args": {}
+
+  value->EndDictionary();  // "allocator name": {}
+}
+
+}  // namespace trace_event
+}  // namespace base