content: Add RendererScheduler.

content/renderer/scheduler/renderer_scheduler_selector.h

+// Copyright 2014 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 CONTENT_RENDERER_SCHEDULER_RENDERER_SCHEDULER_POLICY_H_
+#define CONTENT_RENDERER_SCHEDULER_RENDERER_SCHEDULER_POLICY_H_
+
+#include "base/task/task_queue_selector.h"
+#include "base/threading/thread_checker.h"
+
+namespace content {
+
+class RendererSchedulerSelector : public base::TaskQueueSelector {
+ public:
+  enum QueuePriority {
+    kControlPriority,
+    kHighPriority,
+    kNormalPriority,
+    kBestEffortPriority,
+    // Must be the last entry.
+    kQueuePriorityCount,
+  };
+
+  RendererSchedulerSelector();
+  virtual ~RendererSchedulerSelector();
+
+  // Set the priority of |queue_id| to |set_priority|.
+  void SetQueuePriority(size_t queue_id, QueuePriority set_priority);
+
+  // Enable the |queue_id| with a priority of |priority|.

[Sami, 2014/10/20 13:31:09]

Are all queues enabled or disabled by default? Probably worth mentioning.

[petrcermak, 2014/10/20 17:43:36]

This is explained on renderer_scheduler_selector.cc:25. Nevertheless, I agree
that it should be mentioned.

[rmcilroy, 2014/10/21 17:21:28]

Done.

+  void EnableQueue(size_t queue_id, QueuePriority priority);
+
+  // Disable the |queue_id|.
+  void DisableQueue(size_t queue_id);
+
+  // TaskQueueSelector implementation:
+  virtual void RegisterWorkQueues(
+      const std::vector<const base::TaskQueue*>& work_queues) override;
+  virtual bool SelectWorkQueueToService(size_t* out_queue_index) override;

[petrcermak, 2014/10/20 17:43:36]

Why is the queue index called "queue_id" when it's an input argument and
"...queue_index" when it's an output argument? This suggests they are two
different types of indices.

[rmcilroy, 2014/10/21 17:21:28]

Good catch. Changed all to queue_index

+
+ private:
+  // Return true if |out_queue_index| indicates the index of the queue with
+  // the oldest pending task from the set of queues of |priority|, or
+  // false if all queues of that priority are empty.
+  bool ChooseOldestWithPriority(
+      QueuePriority priority, size_t* out_queue_index);
+
+  // Returns true if |out_queue_index| indicates the index of the control queue,
+  // or false if there is no control queue.
+  bool ControlQueueId(size_t* out_queue_index);

[Sami, 2014/10/20 13:31:09]

Unused?

[rmcilroy, 2014/10/21 17:21:28]

Removed, thanks.

+
+  // Returns true if |queue_id| is enabled with the given |priority|.
+  bool QueueEnabledWithPriority(size_t queue_id, QueuePriority priority);

[Sami, 2014/10/20 13:31:09]

nit: const

[rmcilroy, 2014/10/21 17:21:28]

Done.

+
+  QueuePriority NextPriorty(QueuePriority priority);

[Sami, 2014/10/20 13:31:09]

typo: Priority

+
+  base::ThreadChecker main_thread_checker_;
+  std::vector<const base::TaskQueue*> work_queues_;
+  size_t queue_priorities_[kQueuePriorityCount];
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_SCHEDULER_RENDERER_SCHEDULER_POLICY_H_