[scheduler] Monitor renderer load level.

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

+#include "platform/scheduler/base/thread_load_tracker.h"
+
+namespace blink {
+namespace scheduler {
+
+namespace {
+
+const int kLoadReportingIntervalInMilliseconds = 1000;
+const int kWaitingPeriodBeforeReportingInSeconds = 10;
+
+}  // namespace
+
+ThreadLoadTracker::ThreadLoadTracker(base::TimeTicks now,
+                                         const Callback& callback)
+    : current_time_(now),
+      next_reporting_time_(now),
+      thread_state_(ThreadState::ACTIVE),
+      last_state_change_time_(now),
+      waiting_period_(
+          base::TimeDelta::FromSeconds(kWaitingPeriodBeforeReportingInSeconds)),
+      reporting_interval_(base::TimeDelta::FromMilliseconds(
+          kLoadReportingIntervalInMilliseconds)),
+      callback_(callback) {}
+
+ThreadLoadTracker::~ThreadLoadTracker() {}
+
+void ThreadLoadTracker::Pause(base::TimeTicks now) {
+  Advance(now, TaskState::IDLE);
+  thread_state_ = ThreadState::PAUSED;
+  last_state_change_time_ = now;
+}
+
+void ThreadLoadTracker::Resume(base::TimeTicks now) {
+  Advance(now, TaskState::IDLE);
+  thread_state_ = ThreadState::ACTIVE;
+  last_state_change_time_ = now;
+}
+
+void ThreadLoadTracker::RecordTaskTime(base::TimeTicks start_time,
+                                         base::TimeTicks end_time) {
+  start_time = std::max(last_state_change_time_, start_time);
+  end_time = std::max(last_state_change_time_, end_time);
+
+  Advance(start_time, TaskState::IDLE);
+  Advance(end_time, TaskState::TASK_RUNNING);
+}
+
+void ThreadLoadTracker::RecordIdle(base::TimeTicks now) {
+  Advance(now, TaskState::IDLE);
+}
+
+void ThreadLoadTracker::Advance(base::TimeTicks now,
+                                TaskState task_state) {
+  // This function advances |current_time_| to now and calls |callback_|
+  // when appropriate.
+  if (current_time_ > now) {
+    return;
+  }
+
+  if (thread_state_ == ThreadState::PAUSED) {
+    // If the load tracker is paused, bail out early.
+    current_time_ = now;
+    next_reporting_time_ = now + reporting_interval_;
+    return;
+  }
+
+  while (true) {

[Sami, 2016/08/22 16:35:40]

nit: while (current_time < now) would make this look a bit less scary :)

[altimin, 2016/08/22 17:02:23]

Done.

+    // Forward current_time_ to the earliest of following:
+    // a) time to call |callback_|
+    // b) requested time to forward (|now|).
+    base::TimeTicks next_current_time = std::min(next_reporting_time_, now);
+
+    base::TimeDelta delta = next_current_time - current_time_;
+
+    // Forward time and recalculate |total_time_| and |total_runtime_|.
+    if (thread_state_ == ThreadState::ACTIVE) {
+      total_time_ += delta;
+      if (task_state == TaskState::TASK_RUNNING) {
+        total_runtime_ += delta;
+      }
+    }
+    current_time_ = next_current_time;
+
+    if (current_time_ == next_reporting_time_) {
+      // Call |callback_| if need and update next callback time.
+      if (thread_state_ == ThreadState::ACTIVE && total_time_ >= waiting_period_) {
+        callback_.Run(current_time_, Load());
+      }
+      next_reporting_time_ += reporting_interval_;
+    } else {
+      // current_time_ == now, and it's time to finish up.
+      break;
+    }
+  }
+}
+
+double ThreadLoadTracker::Load() {
+  if (total_time_.is_zero()) {
+    return 0;
+  }
+  return total_runtime_.InSecondsF() / total_time_.InSecondsF();
+}
+
+}  // namespace scheduler
+}  // namespace blink