tracing: the client lib of the tracing service

services/resource_coordinator/public/cpp/tracing/chrome_agent.cc

+// Copyright 2017 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 "services/resource_coordinator/public/cpp/tracing/chrome_agent.h"
+
+#include "base/bind.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/ref_counted_memory.h"
+#include "base/strings/string_util.h"
+#include "base/trace_event/trace_log.h"
+#include "base/values.h"
+#include "services/service_manager/public/cpp/connector.h"
+
+namespace tracing {
+
+// static
+ChromeAgent* ChromeAgent::GetOrCreateInstance(
+    mojom::AgentRegistryPtr agent_registry) {
+  static ChromeAgent* instance = nullptr;
+  if (!instance) {
+    DCHECK(agent_registry);
+    instance = new ChromeAgent(std::move(agent_registry));
+  }
+  return instance;
+}
+
+ChromeAgent::ChromeAgent(mojom::AgentRegistryPtr agent_registry)
+    : binding_(this) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  // agent_registry can be null in tests. The constructor is private and cannot
+  // be directly used in non-test scenarios. GetOrCreateInstance makes sure that
+  // the constructor is called with a non-null agent_registry.
+  if (!agent_registry)
+    return;
+  agent_registry->RegisterAgent(binding_.CreateInterfacePtrAndBind(),
+                                "traceEvents", mojom::TraceDataType::ARRAY,
+                                false /* supports_explicit_clock_sync */);
+}
+
+ChromeAgent::~ChromeAgent() {
+  if (base::trace_event::TraceLog::GetInstance()->IsEnabled())
+    StopAndFlush();
+}
+
+void ChromeAgent::AddMetadataGeneratorFunction(
+    MetadataGeneratorFunction generator) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  metadata_generator_functions_.push_back(generator);
+}
+
+void ChromeAgent::StartTracing(const std::string& config,
+                               mojom::RecorderPtr recorder,
+                               const StartTracingCallback& callback) {
+  DCHECK(!recorder_);
+  recorder_ = std::move(recorder);
+  if (!base::trace_event::TraceLog::GetInstance()->IsEnabled()) {
+    base::trace_event::TraceLog::GetInstance()->SetEnabled(
+        base::trace_event::TraceConfig(config),
+        base::trace_event::TraceLog::RECORDING_MODE);
+  }
+  callback.Run();
+}
+
+void ChromeAgent::StopAndFlush() {
+  base::trace_event::TraceLog::GetInstance()->SetDisabled();
+  if (!recorder_)
+    return;
+  base::trace_event::TraceLog::GetInstance()->Flush(
+      base::Bind(&ChromeAgent::SendChunk, base::Unretained(this)));
+}
+
+void ChromeAgent::RequestClockSyncMarker(
+    const std::string& sync_id,
+    const RequestClockSyncMarkerCallback& callback) {
+  NOTREACHED() << "This agent does not support explicit clock sync";
+}
+
+void ChromeAgent::RequestBufferStatus(
+    const RequestBufferStatusCallback& callback) {
+  auto status = base::trace_event::TraceLog::GetInstance()->GetStatus();
+  callback.Run(status.event_capacity, status.event_count);
+}
+
+void ChromeAgent::GetCategories(const GetCategoriesCallback& callback) {
+  std::vector<std::string> category_vector;
+  base::trace_event::TraceLog::GetInstance()->GetKnownCategoryGroups(
+      &category_vector);
+  callback.Run(base::JoinString(category_vector, ","));
+}
+
+void ChromeAgent::SendChunk(

[Primiano Tucci (use gerrit), 2017/05/16 04:45:11]

minor comment: I'd probably call this OnTraceLogFlush.
The problem I have with SendChunk is that is not immediate to figure out the
direction (who sends the chunk where)

[chiniforooshan, 2017/05/16 15:14:44]

Done.

+    const scoped_refptr<base::RefCountedString>& events_str,
+    bool has_more_events) {
+  DCHECK(recorder_);

[Primiano Tucci (use gerrit), 2017/05/16 04:45:11]

I think the pattern is to not add dhcecks if we are going to dereference the
pointer below and crash anyways.

[chiniforooshan, 2017/05/16 15:14:45]

Done.

+  if (!events_str->data().empty())
+    recorder_->AddChunk(events_str->data());
+  if (!has_more_events) {
+    for (const auto& generator : metadata_generator_functions_) {
+      auto metadata = generator.Run();
+      if (metadata)
+        recorder_->AddMetadata(std::move(metadata));
+    }
+    recorder_.reset();
+  }
+}
+
+}  // namespace tracing