base: Add blame context

base/trace_event/blame_context.cc

+// Copyright 2016 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/blame_context.h"
+
+#include "base/strings/stringprintf.h"
+#include "base/trace_event/trace_event.h"
+#include "base/trace_event/trace_event_argument.h"
+
+namespace base {
+namespace trace_event {
+
+BlameContext::BlameContext(const char* category,
+                           const char* name,
+                           const char* type,
+                           const char* scope,
+                           int64_t id)
+    : category_(category),
+      name_(name),
+      type_(type),
+      scope_(scope),
+      id_(id),
+      parent_scope_(nullptr),
+      parent_id_(0) {
+  Initialize();
+}
+
+BlameContext::BlameContext(const char* category,
+                           const char* name,
+                           const char* type,
+                           const char* scope,
+                           int64_t id,
+                           const BlameContext& parent_context)
+    : category_(category),
+      name_(name),
+      type_(type),
+      scope_(scope),
+      id_(id),
+      parent_scope_(parent_context.scope()),
+      parent_id_(parent_context.id()) {
+  DCHECK(!std::strcmp(name_, parent_context.name()))
+      << "Parent blame context must have the same name";
+  Initialize();
+}
+
+BlameContext::~BlameContext() {
+  TRACE_EVENT_API_ADD_TRACE_EVENT(
+      TRACE_EVENT_PHASE_DELETE_OBJECT, category_group_enabled_, type_, scope_,
+      id_, 0, nullptr, nullptr, nullptr, nullptr, TRACE_EVENT_FLAG_HAS_ID);
+  trace_event::TraceLog::GetInstance()->RemoveEnabledStateObserver(this);
+}
+
+void BlameContext::Enter() {
+  int num_args = 0;
+  TRACE_EVENT_API_ADD_TRACE_EVENT(TRACE_EVENT_PHASE_ENTER_CONTEXT,
+                                  category_group_enabled_, name_, scope_, id_,
+                                  num_args, nullptr, nullptr, nullptr, nullptr,

[Primiano Tucci (use gerrit), 2016/03/21 14:26:29]

or just 0 /* num_args */ if you prefer :)

[Sami, 2016/03/21 15:05:08]

Done.

+                                  TRACE_EVENT_FLAG_HAS_ID);
+}
+
+void BlameContext::Leave() {
+  int num_args = 0;
+  TRACE_EVENT_API_ADD_TRACE_EVENT(TRACE_EVENT_PHASE_LEAVE_CONTEXT,
+                                  category_group_enabled_, name_, scope_, id_,
+                                  num_args, nullptr, nullptr, nullptr, nullptr,
+                                  TRACE_EVENT_FLAG_HAS_ID);
+}
+
+void BlameContext::TakeSnapshot() {
+  if (!*category_group_enabled_)
+    return;
+  scoped_ptr<trace_event::TracedValue> snapshot(new trace_event::TracedValue);
+  AsValueInto(snapshot.get());
+  static const char* kArgName = "snapshot";
+  int num_args = 1;

[Primiano Tucci (use gerrit), 2016/03/21 14:26:29]

nit: kNumArgs?

[Sami, 2016/03/21 15:05:08]

Done.

+  unsigned char arg_types[1] = {TRACE_VALUE_TYPE_CONVERTABLE};
+  scoped_ptr<trace_event::ConvertableToTraceFormat> arg_values[1] = {
+      std::move(snapshot)};
+  TRACE_EVENT_API_ADD_TRACE_EVENT(TRACE_EVENT_PHASE_SNAPSHOT_OBJECT,
+                                  category_group_enabled_, type_, scope_, id_,
+                                  num_args, &kArgName, arg_types, nullptr,
+                                  arg_values, TRACE_EVENT_FLAG_HAS_ID);
+}
+
+void BlameContext::OnTraceLogEnabled() {
+  TakeSnapshot();

[Primiano Tucci (use gerrit), 2016/03/21 14:26:29]

What is the reason for this? Is it to make it so that your BlameContext is
always dumped?
IIRC OnTraceLogEnabled is NOT invoked if you register the observer after tracing
has started *

Does this mean that if you create a BlameContext after tracing has started you
will miss the snapshot?

* I am looking at my own comment in
https://code.google.com/p/chromium/codesearch#chromium/src/base/trace_event/m...

[Sami, 2016/03/21 15:05:08]

Changed to require users to call Initialize() like we discussed.

+}
+
+void BlameContext::OnTraceLogDisabled() {}
+
+void BlameContext::AsValueInto(trace_event::TracedValue* state) {
+  if (!parent_id_)
+    return;
+  state->BeginDictionary("parent");
+  state->SetString("id_ref", StringPrintf("0x%" PRIx64, parent_id_));
+  state->SetString("scope", parent_scope_);
+  state->EndDictionary();
+}
+
+void BlameContext::Initialize() {
+  category_group_enabled_ =
+      TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(category_);
+  TRACE_EVENT_API_ADD_TRACE_EVENT(
+      TRACE_EVENT_PHASE_CREATE_OBJECT, category_group_enabled_, type_, scope_,
+      id_, 0, nullptr, nullptr, nullptr, nullptr, TRACE_EVENT_FLAG_HAS_ID);
+  trace_event::TraceLog::GetInstance()->AddEnabledStateObserver(this);
+}
+
+}  // namespace trace_event
+}  // namespace base