cancelable_task_tracker.h | Explore in Territory

// Copyright 2014 The Chromium Authors
// 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 OnceClosure) 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 OnceClosure).
// After the task is run on the TaskRunner, |reply| will be posted back to
// originating TaskRunner.
//
// NOTE:
//
// CancelableOnceCallback (base/cancelable_callback.h) and WeakPtr binding are
// preferred solutions for canceling a task. However, they don't support
// 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 inputted 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. A CancelableTaskTracker object must be created, used, and destroyed on a
//    single sequence.
//
// 2. It's safe to destroy a CancelableTaskTracker while there are outstanding
//    tasks. This is commonly used to cancel all outstanding tasks.
//
// 3. The task is deleted on the target sequence, and the 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 <memory>
#include <utility>

#include "base/base_export.h"
#include "base/containers/small_map.h"
#include "base/functional/bind.h"
#include "base/functional/callback.h"
#include "base/functional/callback_helpers.h"
#include "base/memory/ref_counted.h"
#include "base/memory/weak_ptr.h"
#include "base/sequence_checker.h"
#include "base/synchronization/atomic_flag.h"
#include "base/task/post_task_and_reply_with_result_internal.h"

namespace base {

class Location;
class ScopedClosureRunner;
class TaskRunner;

class BASE_EXPORT CancelableTaskTracker { … };

}  // namespace base

#endif  // BASE_TASK_CANCELABLE_TASK_TRACKER_H_
chromium/base/task/cancelable_task_tracker.h
