[scheduler] Monitor renderer load level.

third_party/WebKit/Source/platform/scheduler/base/thread_load_tracker.h

+// 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.
+
+#ifndef THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_RENDERER_RENDERER_LOAD_TRACKER_H_
+#define THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_RENDERER_RENDERER_LOAD_TRACKER_H_
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/time/time.h"
+#include "public/platform/WebCommon.h"
+
+namespace blink {
+namespace scheduler {
+
+// This class tracks thread load level, i.e. percentage of wall time spent
+// running tasks.
+// In order to avoid bias it reports load level at regular intervals.
+class BLINK_PLATFORM_EXPORT ThreadLoadTracker {
+ public:
+  // Callback is called with (current_time, load_level) parameters.
+  using Callback = base::Callback<void(base::TimeTicks, double)>;
+
+  ThreadLoadTracker(base::TimeTicks now, const Callback& callback);
+  ~ThreadLoadTracker();
+
+  void Pause(base::TimeTicks now);
+  void Resume(base::TimeTicks now);
+
+  void RecordTaskTime(base::TimeTicks start_time, base::TimeTicks end_time);
+
+  void RecordIdle(base::TimeTicks now);
+
+  // TODO(altimin): Count wakeups.
+
+ private:
+  enum class ThreadState { ACTIVE, PAUSED };
+
+  enum class TaskState { TASK_RUNNING, IDLE };
+
+  // This function advances |time_| to |now|, calling |callback_|
+  // in the process (multiple times if needed).
+  void Advance(base::TimeTicks now, TaskState task_state);
+
+  double Load();
+
+  // |time_| is the last timestamp LoadTracker knows about.
+  base::TimeTicks time_;
+  base::TimeTicks next_reporting_time_;
+
+  ThreadState thread_state_;
+  base::TimeTicks last_state_change_time_;
+
+  base::TimeDelta total_time_;
+  base::TimeDelta total_runtime_;
+
+  // Start reporting values after |waiting_period_|.
+  base::TimeDelta waiting_period_;
+  base::TimeDelta reporting_interval_;
+
+  Callback callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(ThreadLoadTracker);
+};
+
+}  // namespace scheduler
+}  // namespace blink
+
+#endif  // THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_RENDERER_RENDERER_LOAD_TRACKER_H_