TaskScheduler [3/9] Task and Sequence

base/task_scheduler/sequence.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 BASE_TASK_SCHEDULER_SEQUENCE_H_
+#define BASE_TASK_SCHEDULER_SEQUENCE_H_
+
+#include <stddef.h>
+
+#include <queue>
+
+#include "base/base_export.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/task_scheduler/scheduler_lock.h"
+#include "base/task_scheduler/sequence_sort_key.h"
+#include "base/task_scheduler/task.h"
+#include "base/task_scheduler/task_traits.h"
+
+namespace base {
+namespace internal {
+
+// A sequence holds tasks that must be executed in posting order. This class is

[robliao, 2016/02/19 02:33:43]

Nit: Linebreak after the period here is okay.

[fdoray, 2016/02/19 14:12:14]

Done.

+// thread-safe.
+class BASE_EXPORT Sequence : public RefCountedThreadSafe<Sequence> {
+ public:
+  Sequence();
+
+  // Adds |task| at the end of the sequence's queue. Returns true if the
+  // sequence was empty before this operation.
+  bool PushTask(scoped_ptr<Task> task);
+
+  // Returns the task in front of the sequence's queue, if any.
+  const Task* PeekTask() const;
+
+  // Removes the task in front of the sequence's queue. Returns true if the
+  // sequence is empty after this operation. Cannot be called on an empty
+  // sequence.
+  bool PopTask();
+
+  // Returns a SequenceSortKey to use when inserting the sequence in a priority
+  // queue. Cannot be called on an empty sequence.
+  SequenceSortKey GetSortKey() const;
+
+ private:
+  friend class RefCountedThreadSafe<Sequence>;
+  ~Sequence();
+
+  // Controls access to all members.

[robliao, 2016/02/19 02:33:43]

Nit: Synchronizes access to all members.

[fdoray, 2016/02/19 14:12:14]

Done.

+  mutable SchedulerLock lock_;
+
+  // Queue of tasks to execute.
+  std::queue<scoped_ptr<Task>> queue_;
+
+  // Number of task priorities in the TaskPriority enum.
+  static const size_t kNumTaskPriorities =

[robliao, 2016/02/19 02:33:43]

Shouldn't this be taken from task_traits.h?

[fdoray, 2016/02/19 14:12:14]

Done.

+      static_cast<TaskPriorityUnderlyingType>(TaskPriority::HIGHEST) + 1;

[robliao, 2016/02/19 02:33:43]

This seems like something that should remain at or near TaskPriority. You can
static_assert(TaskPriority::HIGHEST == kNumTaskPriorities + 1) in the
implementation file.

[fdoray, 2016/02/19 14:12:14]

Done.

+
+  // Number of tasks contained in the sequence for each priority.
+  size_t num_tasks_per_priority_[kNumTaskPriorities] = {};
+
+  DISALLOW_COPY_AND_ASSIGN(Sequence);
+};
+
+}  // namespace internal
+}  // namespace base
+
+#endif  // BASE_TASK_SCHEDULER_SEQUENCE_H_