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 {

[gab, 2016/04/07 21:32:08]

Does it make sense to hook it up to SchedulerThreadPool in this CL or is that a
big enough change to warrant its own CL? I guess it needs the service thread to
be functional so we have to wait?

[fdoray, 2016/04/08 17:24:51]

We need the service thread for this to be functional.

+ 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);

[gab, 2016/04/07 21:32:08]

on_next_delayed_run_time_updated ?

(to make it clear it's a notification and to reflect GetNextDelayedRunTime())

[fdoray, 2016/04/08 17:24:51]

Done.

+  ~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|.

[gab, 2016/04/07 21:32:08]

s/with the current time being great or equal to |task->delayed_run_time|/while
Now() is passed |task->delayed_run_time|/ ?

[fdoray, 2016/04/08 17:24:51]

Done.

+  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:
+  struct DelayedTask;
+  struct DelayedTaskComparator {
+    bool operator()(const DelayedTask& left, const DelayedTask& right) const;
+  };
+
+  // Returns the current time. Can be overridden for tests.
+  virtual TimeTicks Now() const;
+
+  const Closure delayed_run_time_changed_;
+
+  // Synchronizes access to all members below.
+  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.
+  using DelayedTaskQueue = std::priority_queue<DelayedTask,
+                                               std::vector<DelayedTask>,
+                                               DelayedTaskComparator>;

[gab, 2016/04/07 21:32:08]

I'm surprised that the definition of DelayedTask isn't required to compile this
template.

[fdoray, 2016/04/08 17:24:51]

The definition of DelayedTask isn't required to compute the size of
DelayedTaskQueue.

+  DelayedTaskQueue 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_