arc: enable Android tracing from chrome://tracing in dev mode

chromeos/trace/arc_trace_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 "chromeos/trace/arc_trace_agent.h"
+
+#include <string>
+
+#include "base/bind.h"
+#include "base/logging.h"
+#include "base/memory/singleton.h"
+#include "base/threading/thread_checker.h"
+#include "base/threading/thread_task_runner_handle.h"
+
+namespace chromeos {
+
+namespace {
+
+constexpr char kArcTracingAgentName[] = "arc";
+constexpr char kArcTraceLabel[] = "ArcTraceEvents";
+
+void OnStopTracing(bool success) {
+  LOG_IF(WARNING, !success) << "Failed to stop ARC tracing.";
+}
+
+class ArcTraceAgentImpl : public ArcTraceAgent {
+ public:
+  // base::trace_event::TracingAgent overrides:
+  std::string GetTracingAgentName() override { return kArcTracingAgentName; }
+
+  std::string GetTraceEventLabel() override { return kArcTraceLabel; }
+
+  void StartAgentTracing(const base::trace_event::TraceConfig& trace_config,
+                         const StartAgentTracingCallback& callback) override {
+    DCHECK(thread_checker_.CalledOnValidThread());
+    // delegate_ may be nullptr if ARC is not enabled on the system. In such
+    // case, simply do nothing.
+    if (!delegate_) {
+      // Use PostTask as the convention of TraceAgent. The caller expects
+      // callback to be called after this function returns.
+      base::ThreadTaskRunnerHandle::Get()->PostTask(
+          FROM_HERE, base::Bind(callback, GetTracingAgentName(), false));
+      return;
+    }
+
+    delegate_->StartTracing(trace_config,
+                            base::Bind(callback, GetTracingAgentName()));
+  }
+
+  void StopAgentTracing(const StopAgentTracingCallback& callback) override {
+    DCHECK(thread_checker_.CalledOnValidThread());
+    if (delegate_)
+      delegate_->StopTracing(base::Bind(OnStopTracing));
+
+    // Trace data is collect via systrace (debugd) in dev-mode. Simply
+    // return empty data here.
+    std::string no_data;
+    callback.Run(GetTracingAgentName(), GetTraceEventLabel(),

[Daniel Erat, 2017/03/07 15:53:21]

this interface seems surprising. why is the callback being invoked synchronously
here? StartAgentTracing runs its callback asynchronously.

[Earl Ou, 2017/03/08 05:03:04]

Changed to PostTask now.

+                 base::RefCountedString::TakeString(&no_data));
+  }
+
+  // ArcTraceAgent overrides:
+  void SetDelegate(Delegate* delegate) override {
+    DCHECK(thread_checker_.CalledOnValidThread());
+    delegate_ = delegate;
+  }
+
+  static ArcTraceAgentImpl* GetInstance() {
+    return base::Singleton<ArcTraceAgentImpl>::get();
+  }
+
+ private:
+  // This allows constructor and destructor to be private and usable only
+  // by the Singleton class.
+  friend struct base::DefaultSingletonTraits<ArcTraceAgentImpl>;
+
+  ArcTraceAgentImpl() = default;
+  ~ArcTraceAgentImpl() override = default;
+
+  Delegate* delegate_ = nullptr;  // Owned by ArcServiceLauncher.
+  base::ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(ArcTraceAgentImpl);
+};
+
+}  // namespace
+
+// static
+ArcTraceAgent* ArcTraceAgent::GetInstance() {
+  return ArcTraceAgentImpl::GetInstance();
+}
+
+ArcTraceAgent::~ArcTraceAgent() = default;
+
+ArcTraceAgent::Delegate::~Delegate() = default;
+
+}  // namespace chromeos