Make CancelableTaskTracker sequence-safe.

base/task/cancelable_task_tracker.h

 // Copyright 2014 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.
 
 // CancelableTaskTracker posts tasks (in the form of a Closure) to a
 // TaskRunner, and is able to cancel the task later if it's not needed
 // anymore.  On destruction, CancelableTaskTracker will cancel all
 // tracked tasks.
 //
 // Each cancelable task can be associated with a reply (also a Closure). After
 // the task is run on the TaskRunner, |reply| will be posted back to
 // originating TaskRunner.
 //
 // NOTE:
 //
 // CancelableCallback (base/cancelable_callback.h) and WeakPtr binding are
 // preferred solutions for canceling a task. However, they don't support
-// cancelation from another thread. This is sometimes a performance critical
+// cancelation from another sequence. This is sometimes a performance critical
 // requirement. E.g. We need to cancel database lookup task on DB thread when
 // user changes inputed text. If it is performance critical to do a best effort
-// cancelation of a task, then CancelableTaskTracker is appropriate,
-// otherwise use one of the other mechanisms.
+// cancelation of a task, then CancelableTaskTracker is appropriate, otherwise
+// use one of the other mechanisms.
 //
 // THREAD-SAFETY:
 //
-// 1. CancelableTaskTracker objects are not thread safe. They must
-// be created, used, and destroyed on the originating thread that posts the
-// task. It's safe to destroy a CancelableTaskTracker while there
-// are outstanding tasks. This is commonly used to cancel all outstanding
-// tasks.
+// 1. A CancelableTaskTracker object must be created, used, and destroyed on a
+//    single sequence.
 //
-// 2. Both task and reply are deleted on the originating thread.
+// 2. It's safe to destroy a CancelableTaskTracker while there are outstanding
+//    tasks. This is commonly used to cancel all outstanding tasks.
 //
-// 3. IsCanceledCallback is thread safe and can be run or deleted on any
-// thread.
+// 3. Both task and reply are deleted on the originating sequence.
+//
+// 4. IsCanceledCallback can be run or deleted on any sequence.
 #ifndef BASE_TASK_CANCELABLE_TASK_TRACKER_H_
 #define BASE_TASK_CANCELABLE_TASK_TRACKER_H_
 
 #include <stdint.h>
 
 #include "base/base_export.h"
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/containers/hash_tables.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/post_task_and_reply_with_result_internal.h"
-#include "base/threading/thread_checker.h"
+#include "base/sequence_checker.h"
 
 namespace tracked_objects {
 class Location;
 }  // namespace tracked_objects
 
 namespace base {
 
 class CancellationFlag;
 class TaskRunner;
 
@@ skipping 65 matching lines @@
   // tracked.
   bool HasTrackedTasks() const;
 
  private:
   void Track(TaskId id, base::CancellationFlag* flag);
   void Untrack(TaskId id);
 
   base::hash_map<TaskId, base::CancellationFlag*> task_flags_;
 
   TaskId next_id_;
-  base::ThreadChecker thread_checker_;
+  SequenceChecker sequence_checker_;
 
   base::WeakPtrFactory<CancelableTaskTracker> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(CancelableTaskTracker);
 };
 
 }  // namespace base
 
 #endif  // BASE_TASK_CANCELABLE_TASK_TRACKER_H_