tracing: the recorder implementation

services/resource_coordinator/tracing/recorder.h

+// 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.
+
+#ifndef SERVICES_RESOURCE_COORDINATOR_TRACING_RECORDER_H_
+#define SERVICES_RESOURCE_COORDINATOR_TRACING_RECORDER_H_
+
+#include "base/callback_forward.h"
+#include "base/logging.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "base/sequenced_task_runner.h"
+#include "base/values.h"
+#include "mojo/public/cpp/bindings/binding.h"
+#include "services/resource_coordinator/public/interfaces/tracing/tracing.mojom.h"
+
+namespace tracing {
+
+class Recorder : public mojom::Recorder {
+ public:
+  // The tracing service creates instances of the |Recorder| class and send them
+  // to agents. The agents then use the recorder for sending trace data to the
+  // tracing service.
+  //
+  // |data_is_array| tells the recorder whether the data is of type array or
+  // string. Chunks of type array are concatenated using a comma as the
+  // separator; chuunks of type string are concatenated without a separator.
+  //
+  // |on_data_change_callback| is run whenever the recorder receives data from
+  // the agent or when the connection is lost to notify the tracing service of
+  // the data change.
+  //
+  // |background_task_runner| is used so that if the tracing service is run on
+  // the UI thread we do not block it. So buffering trace events and copying
+  // them to data pipes are done on a background thread.
+  Recorder(
+      mojom::RecorderRequest request,
+      bool data_is_array,
+      const base::Closure& on_data_change_callback,
+      const scoped_refptr<base::SequencedTaskRunner>& background_task_runner);
+  ~Recorder() override;
+
+  const std::string& data() const {
+    // All access to |data_| should be done on the background thread.
+    DCHECK(background_task_runner_->RunsTasksOnCurrentThread());
+    return data_;
+  }
+
+  void clear_data() {
+    // All access to |data_| should be done on the background thread.
+    DCHECK(background_task_runner_->RunsTasksOnCurrentThread());
+    data_.clear();
+  }
+
+  const base::DictionaryValue& metadata() const { return metadata_; }
+  bool is_recording() const { return is_recording_; }
+  bool data_is_array() const { return data_is_array_; }
+
+ private:
+  friend class RecorderTest;  // For testing.
+  // mojom::Recorder
+  // These are called by agents for sending trace data to the tracing service.
+  void AddChunk(const std::string& chunk) override;
+  void AddMetadata(std::unique_ptr<base::DictionaryValue> metadata) override;
+
+  void OnConnectionError();
+
+  std::string data_;
+  base::DictionaryValue metadata_;
+  bool is_recording_;
+  bool data_is_array_;
+  base::Closure on_data_change_callback_;
+  // To avoid blocking the UI thread if the tracing service is run on the UI
+  // thread, we make sure that buffering trace events and copying them to the
+  // final stream is done on a background thread.
+  scoped_refptr<base::SequencedTaskRunner> background_task_runner_;
+  mojo::Binding<mojom::Recorder> binding_;
+  base::WeakPtrFactory<Recorder> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(Recorder);
+};
+
+}  // namespace tracing
+#endif  // SERVICES_RESOURCE_COORDINATOR_TRACING_RECORDER_H_