Move CancelableTaskTracker to //base/task/CancelableTaskTracker.

chrome/common/cancelable_task_tracker.h

-// Copyright (c) 2012 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
-// 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.
-//
-// 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.
-//
-// 2. Both task and reply are deleted on the originating thread.
-//
-// 3. IsCanceledCallback is thread safe and can be run or deleted on any thread.
-
-#ifndef CHROME_COMMON_CANCELABLE_TASK_TRACKER_H_
-#define CHROME_COMMON_CANCELABLE_TASK_TRACKER_H_
-
-#include "base/basictypes.h"
-#include "base/callback.h"
-#include "base/containers/hash_tables.h"
-#include "base/memory/weak_ptr.h"
-#include "base/threading/thread_checker.h"
-
-namespace base {
-class CancellationFlag;
-class TaskRunner;
-}  // namespace base
-
-namespace tracked_objects {
-class Location;
-}  // namespace tracked_objects
-
-class CancelableTaskTracker {
- public:
-  // All values except kBadTaskId are valid.
-  typedef int64 TaskId;
-  static const TaskId kBadTaskId;
-
-  typedef base::Callback<bool()> IsCanceledCallback;
-
-  CancelableTaskTracker();
-
-  // Cancels all tracked tasks.
-  ~CancelableTaskTracker();
-
-  TaskId PostTask(base::TaskRunner* task_runner,
-                  const tracked_objects::Location& from_here,
-                  const base::Closure& task);
-
-  TaskId PostTaskAndReply(base::TaskRunner* task_runner,
-                          const tracked_objects::Location& from_here,
-                          const base::Closure& task,
-                          const base::Closure& reply);
-
-  // Creates a tracked TaskId and an associated IsCanceledCallback. Client can
-  // later call TryCancel() with the returned TaskId, and run |is_canceled_cb|
-  // from any thread to check whether the TaskId is canceled.
-  //
-  // The returned task ID is tracked until the last copy of
-  // |is_canceled_cb| is destroyed.
-  //
-  // Note. This function is used to address some special cancelation requirement
-  // in existing code. You SHOULD NOT need this function in new code.
-  TaskId NewTrackedTaskId(IsCanceledCallback* is_canceled_cb);
-
-  // After calling this function, |task| and |reply| will not run. If the
-  // cancelation happens when |task| is running or has finished running, |reply|
-  // will not run. If |reply| is running or has finished running, cancellation
-  // is a noop.
-  //
-  // Note. It's OK to cancel a |task| for more than once. The later calls are
-  // noops.
-  void TryCancel(TaskId id);
-
-  // It's OK to call this function for more than once. The later calls are
-  // noops.
-  void TryCancelAll();
-
-  // Returns true iff there are in-flight tasks that are still being
-  // tracked.
-  bool HasTrackedTasks() const;
-
- private:
-  void Track(TaskId id, base::CancellationFlag* flag);
-  void Untrack(TaskId id);
-
-  base::hash_map<TaskId, base::CancellationFlag*> task_flags_;
-  base::WeakPtrFactory<CancelableTaskTracker> weak_factory_;
-
-  TaskId next_id_;
-  base::ThreadChecker thread_checker_;
-
-  DISALLOW_COPY_AND_ASSIGN(CancelableTaskTracker);
-};
-
-#endif  // CHROME_COMMON_CANCELABLE_TASK_TRACKER_H_