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();
+
+  // Synchronously shuts down the task tracker. Once this is called, only tasks
+  // posted with 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| by calling |post_task_callback| unless the current shutdown
+  // state prevents that. A task forwarded to |post_task_callback| must be
+  // handed off to this class' RunTask() when it is to be executed.

[gab, 2016/03/09 21:53:25]

s/handed off/handed back/

[fdoray, 2016/03/15 17:28:09]

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() first.
+  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:
+  // Called before a task with |shutdown_behavior| is handed off to
+  // |post_task_callback| by PostTask(). Updates |num_tasks_blocking_shutdown_|
+  // and returns true if the current shutdown state allows the task to be
+  // posted.
+  bool BeforePostTask(TaskShutdownBehavior shutdown_behavior);
+
+  // Called before a task with |shutdown_behavior| is run by RunTask(). Updates
+  // |num_tasks_blocking_shutdown_| and returns true if the current shutdown
+  // state allows the task to be run.
+  bool BeforeRunTask(TaskShutdownBehavior shutdown_behavior);
+
+  // Called after a task with |shutdown_behavior| has been run by RunTask().
+  // Updates |num_tasks_blocking_shutdown_| and signals |cv_| when appropriate.
+  void AfterRunTask(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_