Task Scheduler.

base/task_scheduler/shutdown_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_SHUTDOWN_MANAGER_H_
+#define BASE_TASK_SCHEDULER_SHUTDOWN_MANAGER_H_
+
+#include "base/base_export.h"
+#include "base/macros.h"
+#include "base/synchronization/condition_variable.h"
+#include "base/task_scheduler/scheduler_lock.h"
+#include "base/task_scheduler/task_traits.h"
+
+namespace base {
+namespace task_scheduler {
+
+// Ensures proper shutdown behavior of the task scheduler. This class is thread-
+// safe.
+class BASE_EXPORT ShutdownManager {
+ public:
+  ShutdownManager();
+
+  // Shuts down the task scheduler. After this is called, only tasks posted with
+  // the BLOCK_SHUTDOWN behavior are scheduled. Returns when:
+  // - All SKIP_ON_SHUTDOWN tasks that were already running have completed their
+  //   execution.
+  // - There is no pending BLOCK_SHUTDOWN tasks.
+  void Shutdown();
+
+  // Indicates whether a task with this |shutdown_behavior| should be posted.
+  bool ShouldPostTask(TaskShutdownBehavior shutdown_behavior);
+
+  // Indicates whether a task with this |shutdown_behavior| should be scheduled.
+  bool ShouldScheduleTask(TaskShutdownBehavior shutdown_behavior);
+
+  // Notifies the shutdown manager that a task with this |shutdown_behavior|
+  // completed its execution.
+  void DidExecuteTask(TaskShutdownBehavior shutdown_behavior);
+
+  // Returns true once Shutdown() has returned. No new task can be scheduled
+  // after this point.
+  bool shutdown_completed() const;
+
+  // Sets |is_shutting_down_| to true. This has the same effect as calling
+  // Shutdown(), but doesn't block.
+  void SetIsShuttingDownForTesting();
+
+  // Returns true once Shutdown() or SetIsShuttingDownForTesting() has been
+  // called.
+  bool is_shutting_down_for_testing() const { return is_shutting_down_; }
+
+ private:
+  // Lock protecting all members.
+  SchedulerLock lock_;
+
+  // Condition variable signaled when |num_tasks_blocking_shutdown_| reaches
+  // zero.
+  ConditionVariable cv_;
+
+  // Number of tasks blocking shutdown.
+  size_t num_tasks_blocking_shutdown_;
+
+  // True once Shutdown() has been called.
+  bool is_shutting_down_;
+
+  bool shutdown_completed_;
+
+  DISALLOW_COPY_AND_ASSIGN(ShutdownManager);
+};
+
+}  // namespace task_scheduler
+}  // namespace base
+
+#endif  // BASE_TASK_SCHEDULER_SHUTDOWN_MANAGER_H_