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/metrics/histogram_base.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 go through the scheduler's 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 scheduler. 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 back to this instance's RunTask() when it is to be executed.
+  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);
+
+  // Returns true while shutdown is in progress (i.e. Shutdown() has been called
+  // but hasn't returned).
+  bool IsShuttingDownForTesting() const;
+
+  bool shutdown_completed() const {
+    AutoSchedulerLock auto_lock(lock_);
+    return shutdown_completed_;
+  }
+
+ private:
+  // Called before a task with |shutdown_behavior| is handed off to
+  // |post_task_callback| by PostTask(). Updates |num_tasks_blocking_shutdown_|
+  // if necessary 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_| if necessary 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 |shutdown_cv_| if
+  // necessary.
+  void AfterRunTask(TaskShutdownBehavior shutdown_behavior);
+
+  // Synchronizes access to all members.
+  mutable SchedulerLock lock_;
+
+  // Condition variable signaled when |num_tasks_blocking_shutdown_| reaches
+  // zero while shutdown is in progress. Null if shutdown isn't in progress.
+  scoped_ptr<ConditionVariable> shutdown_cv_;
+
+  // Number of tasks blocking shutdown.
+  size_t num_tasks_blocking_shutdown_ = 0;
+
+  // Number of BLOCK_SHUTDOWN tasks posted during shutdown.
+  HistogramBase::Sample num_block_shutdown_tasks_posted_during_shutdown_ = 0;
+
+  // True once Shutdown() has returned. No new task can be scheduled after this.
+  bool shutdown_completed_ = false;
+
+  DISALLOW_COPY_AND_ASSIGN(TaskTracker);
+};
+
+}  // namespace internal
+}  // namespace base
+
+#endif  // BASE_TASK_SCHEDULER_TASK_TRACKER_H_