TaskScheduler [9] Delayed Task Manager

base/task_scheduler/delayed_task_manager.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_DELAYED_TASK_MANAGER_H_
+#define BASE_TASK_SCHEDULER_DELAYED_TASK_MANAGER_H_
+
+#include <stddef.h>
+
+#include <memory>
+#include <queue>
+#include <vector>
+
+#include "base/base_export.h"
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/task_scheduler/scheduler_lock.h"
+#include "base/task_scheduler/task.h"
+#include "base/time/time.h"
+
+namespace base {
+namespace internal {
+
+// A DelayedTaskManager holds delayed tasks until they become ripe for
+// execution. When they become ripe for execution, it invokes a custom
+// callback. This class is thread-safe.
+class BASE_EXPORT DelayedTaskManager {
+ public:
+  using PostTaskCallback = Callback<void(std::unique_ptr<Task>)>;
+
+  // |delayed_run_time_changed| is invoked when the next delayed run time
+  // changes as a result of adding a new delayed task to the manager.
+  explicit DelayedTaskManager(const Closure& delayed_run_time_changed);
+  ~DelayedTaskManager();
+
+  // Adds |task| to a queue of delayed tasks. |post_task_callback| will be
+  // invoked the first time that PostReadyTasks() is called with the current
+  // time being greater or equal to |task->delayed_run_time|.
+  void AddDelayedTask(std::unique_ptr<Task> task,
+                      const PostTaskCallback& post_task_callback);
+
+  // Posts delayed tasks that are ripe for execution.
+  void PostReadyTasks();
+
+  // Returns the next time at which a delayed task will become ripe for
+  // execution, or a null TimeTicks if there is no pending delayed tasks.
+  TimeTicks GetNextDelayedRunTime() const;
+
+ private:
+  // Returns the current time. Can be overridden for tests.
+  virtual TimeTicks Now();

[robliao, 2016/04/04 17:59:53]

Nit: This can be const.

[fdoray, 2016/04/04 19:52:19]

Done.

+
+  struct DelayedTask;

[robliao, 2016/04/04 17:59:53]

Nit: Move this struct and the one below to the top of the private block.

[fdoray, 2016/04/04 19:52:19]

Done.

+  struct DelayedTaskComparator {
+    bool operator()(const DelayedTask& left, const DelayedTask& right) const;
+  };
+
+  const Closure delayed_run_time_changed_;
+
+  // Synchronizes acces to all members below.

[robliao, 2016/04/04 17:59:53]

Nit: access

[fdoray, 2016/04/04 19:52:19]

Done.

+  mutable SchedulerLock lock_;
+
+  // Priority queue of delayed tasks. The delayed task with the smallest
+  // |task->delayed_run_time| is in front of the priority queue.
+  std::priority_queue<DelayedTask,

[robliao, 2016/04/04 17:59:53]

Nit: This might be more readable as a type.

using DelayedTasksQueue = std::priority_queue<...>
DelayedTasksQueue delayed_tasks_;

[fdoray, 2016/04/04 19:52:19]

Done.

+                      std::vector<DelayedTask>,
+                      DelayedTaskComparator>
+      delayed_tasks_;
+
+  // The index to assign to the next delayed task added to the manager.
+  size_t next_delayed_task_index_ = 0;
+
+  DISALLOW_COPY_AND_ASSIGN(DelayedTaskManager);
+};
+
+}  // namespace internal
+}  // namespace base
+
+#endif  // BASE_TASK_SCHEDULER_DELAYED_TASK_MANAGER_H_