TaskScheduler [5/9] Task Tracker

base/task_scheduler/task_tracker.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_TASK_TRACKER_H_
+#define BASE_TASK_SCHEDULER_TASK_TRACKER_H_
+
+#include "base/base_export.h"
+#include "base/callback_forward.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/synchronization/condition_variable.h"
+#include "base/task_scheduler/scheduler_lock.h"
+#include "base/task_scheduler/task.h"
+#include "base/task_scheduler/task_traits.h"
+
+namespace base {
+namespace internal {
+
+// All tasks of the scheduler go through a TaskTracker when they are posted and
+// when they are executed. The TaskTracker enforces shutdown semantics and takes
+// care of tracing and profiling. This class is thread-safe.
+class BASE_EXPORT TaskTracker {
+ public:
+  TaskTracker();
+  ~TaskTracker();
+
+  // Shuts down the task tracker. Once this is called, only tasks posted with

[robliao, 2016/03/01 22:29:41]

The blocking behavior is important enough to reemphasize. Let's add
Synchronously  shutdown down the task tracker.

[fdoray, 2016/03/02 00:38:41]

Done.

+  // the BLOCK_SHUTDOWN behavior will be run. Returns when:
+  // - All SKIP_ON_SHUTDOWN tasks that were already running have completed their
+  //   execution.
+  // - All posted BLOCK_SHUTDOWN tasks have completed their execution.
+  // This must only be called once.
+  void Shutdown();
+
+  // Posts |task| unless the current shutdown state prevents that. Posting a

[robliao, 2016/03/01 22:29:41]

Calls |post_task_callback| unless the current shutdown state prevents that.

[fdoray, 2016/03/02 00:38:41]

Done.

+  // task involves updating the internal state of the TaskTracker, generating a
+  // tracing event and invoking |post_task_callback|. |post_task_callback| must

[gab, 2016/03/01 22:18:47]

',' before "and"

[fdoray, 2016/03/02 00:38:41]

Done. (Conflicts with robliao@'s comment)

+  // add the task it receives to a pool from which tasks are run until
+  // shutdown_completed() returns true.

[gab, 2016/03/01 22:18:47]

s/are run until shutdown_completed() returns true/are handed off to this class'
RunTask() when they are to be executed/

It's important that those tasks make it back through RunTask() -- and it's not
otherwise relevant to this API when the pool exits.

[fdoray, 2016/03/02 00:38:41]

Done.

+  void PostTask(const Callback<void(scoped_ptr<Task>)>& post_task_callback,
+                scoped_ptr<Task> task);
+
+  // Runs |task| unless the current shutdown state prevents that. |task| must
+  // have been successfully posted via PostTask().

[gab, 2016/03/01 22:18:47]

s/./ first./

[fdoray, 2016/03/02 00:38:41]

Done.

+  void RunTask(const Task* task);
+
+  bool shutdown_completed() const {
+    AutoSchedulerLock auto_lock(lock_);
+    return shutdown_completed_;
+  }
+
+  bool is_shutting_down_for_testing() const {
+    AutoSchedulerLock auto_lock(lock_);
+    return is_shutting_down_;
+  }
+
+ private:
+  // Informs TaskTracker that a task with |shutdown_behavior| is about to be
+  // posted. Updates |num_tasks_blocking_shutdown_| and returns true if this
+  // is allowed by the current shutdown state.
+  bool RequestPostTask(TaskShutdownBehavior shutdown_behavior);
+
+  // Informs TaskTracker that a task with |shutdown_behavior| is about to be
+  // scheduled. Updates |num_tasks_blocking_shutdown_| and returns true if this
+  // is allowed by the current shutdown state.
+  bool RequestScheduleTask(TaskShutdownBehavior shutdown_behavior);
+
+  // Informs TaskTracker that a task with |shutdown_behavior| has been executed.
+  // Updates |num_tasks_blocking_shutdown_| and signals |cv_| when appropriate.
+  void DidExecuteTask(TaskShutdownBehavior shutdown_behavior);
+
+  // Synchronizes access to all members.
+  mutable SchedulerLock lock_;
+
+  // Condition variable signaled when |num_tasks_blocking_shutdown_| reaches
+  // zero while |is_shutting_down_|.
+  scoped_ptr<ConditionVariable> cv_;
+
+  // Number of tasks blocking shutdown.
+  size_t num_tasks_blocking_shutdown_;
+
+  // True when Shutdown() is waiting for tasks blocking shutdown to complete
+  // their execution.
+  bool is_shutting_down_;
+
+  // True once Shutdown() has returned. No new task can be scheduled after this.
+  bool shutdown_completed_;
+
+  DISALLOW_COPY_AND_ASSIGN(TaskTracker);
+};
+
+}  // namespace internal
+}  // namespace base
+
+#endif  // BASE_TASK_SCHEDULER_TASK_TRACKER_H_