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| 1 // Copyright 2014 The Chromium Authors. All rights reserved. | |
| 2 // Use of this source code is governed by a BSD-style license that can be | |
| 3 // found in the LICENSE file. | |
| 4 | |
| 5 // CancelableTaskTracker posts tasks (in the form of a Closure) to a | |
| 6 // TaskRunner, and is able to cancel the task later if it's not needed | |
| 7 // anymore. On destruction, CancelableTaskTracker will cancel all | |
| 8 // tracked tasks. | |
| 9 // | |
| 10 // Each cancelable task can be associated with a reply (also a Closure). After | |
| 11 // the task is run on the TaskRunner, |reply| will be posted back to | |
| 12 // originating TaskRunner. | |
| 13 // | |
| 14 // NOTE: | |
| 15 // | |
| 16 // CancelableCallback (base/cancelable_callback.h) and WeakPtr binding are | |
| 17 // preferred solutions for canceling a task. However, they don't support | |
| 18 // cancelation from another thread. This is sometimes a performance critical | |
| 19 // requirement. E.g. We need to cancel database lookup task on DB thread when | |
| 20 // user changes inputed text. If it is performance critical to do a best effort | |
| 21 // cancelation of a task, then CancelableTaskTracker is appropriate, | |
| 22 // otherwise use one of the other mechanisms. | |
| 23 // | |
| 24 // THREAD-SAFETY: | |
| 25 // | |
| 26 // 1. CancelableTaskTracker objects are not thread safe. They must | |
| 27 // be created, used, and destroyed on the originating thread that posts the | |
| 28 // task. It's safe to destroy a CancelableTaskTracker while there | |
| 29 // are outstanding tasks. This is commonly used to cancel all outstanding | |
| 30 // tasks. | |
| 31 // | |
| 32 // 2. Both task and reply are deleted on the originating thread. | |
| 33 // | |
| 34 // 3. IsCanceledCallback is thread safe and can be run or deleted on any | |
| 35 // thread. | |
| 36 #ifndef BASE_TASK_CANCELABLE_TASK_TRACKER_H_ | |
| 37 #define BASE_TASK_CANCELABLE_TASK_TRACKER_H_ | |
| 38 | |
| 39 #include "base/base_export.h" | |
| 40 #include "base/basictypes.h" | |
| 41 #include "base/callback.h" | |
| 42 #include "base/containers/hash_tables.h" | |
| 43 #include "base/memory/weak_ptr.h" | |
| 44 #include "base/task_runner_util.h" | |
| 45 #include "base/threading/thread_checker.h" | |
| 46 | |
| 47 namespace tracked_objects { | |
| 48 class Location; | |
| 49 } // namespace tracked_objects | |
| 50 | |
| 51 namespace base { | |
| 52 | |
| 53 class CancellationFlag; | |
| 54 class TaskRunner; | |
| 55 | |
| 56 class BASE_EXPORT CancelableTaskTracker { | |
| 57 public: | |
| 58 // All values except kBadTaskId are valid. | |
| 59 typedef int64 TaskId; | |
| 60 static const TaskId kBadTaskId; | |
| 61 | |
| 62 typedef base::Callback<bool()> IsCanceledCallback; | |
| 63 | |
| 64 CancelableTaskTracker(); | |
| 65 | |
| 66 // Cancels all tracked tasks. | |
| 67 ~CancelableTaskTracker(); | |
| 68 | |
| 69 TaskId PostTask(base::TaskRunner* task_runner, | |
| 70 const tracked_objects::Location& from_here, | |
| 71 const base::Closure& task); | |
| 72 | |
| 73 TaskId PostTaskAndReply(base::TaskRunner* task_runner, | |
| 74 const tracked_objects::Location& from_here, | |
| 75 const base::Closure& task, | |
| 76 const base::Closure& reply); | |
| 77 | |
| 78 template <typename TaskReturnType, typename ReplyArgType> | |
| 79 TaskId PostTaskAndReplyWithResult( | |
| 80 base::TaskRunner* task_runner, | |
| 81 const tracked_objects::Location& from_here, | |
| 82 const base::Callback<TaskReturnType(void)>& task, | |
| 83 const base::Callback<void(ReplyArgType)>& reply) { | |
| 84 TaskReturnType* result = new TaskReturnType(); | |
| 85 return PostTaskAndReply( | |
| 86 task_runner, | |
| 87 from_here, | |
| 88 base::Bind(&base::internal::ReturnAsParamAdapter<TaskReturnType>, | |
| 89 task, | |
| 90 base::Unretained(result)), | |
| 91 base::Bind(&base::internal::ReplyAdapter<TaskReturnType, ReplyArgType>, | |
| 92 reply, | |
| 93 base::Owned(result))); | |
| 94 } | |
| 95 | |
| 96 // Creates a tracked TaskId and an associated IsCanceledCallback. Client can | |
| 97 // later call TryCancel() with the returned TaskId, and run |is_canceled_cb| | |
| 98 // from any thread to check whether the TaskId is canceled. | |
| 99 // | |
| 100 // The returned task ID is tracked until the last copy of | |
| 101 // |is_canceled_cb| is destroyed. | |
| 102 // | |
| 103 // Note. This function is used to address some special cancelation requirement | |
| 104 // in existing code. You SHOULD NOT need this function in new code. | |
| 105 TaskId NewTrackedTaskId(IsCanceledCallback* is_canceled_cb); | |
| 106 | |
| 107 // After calling this function, |task| and |reply| will not run. If the | |
| 108 // cancelation happens when |task| is running or has finished running, |reply| | |
| 109 // will not run. If |reply| is running or has finished running, cancellation | |
| 110 // is a noop. | |
| 111 // | |
| 112 // Note. It's OK to cancel a |task| for more than once. The later calls are | |
| 113 // noops. | |
| 114 void TryCancel(TaskId id); | |
| 115 | |
| 116 // It's OK to call this function for more than once. The later calls are | |
| 117 // noops. | |
| 118 void TryCancelAll(); | |
| 119 | |
| 120 // Returns true iff there are in-flight tasks that are still being | |
| 121 // tracked. | |
| 122 bool HasTrackedTasks() const; | |
| 123 | |
| 124 private: | |
| 125 void Track(TaskId id, base::CancellationFlag* flag); | |
| 126 void Untrack(TaskId id); | |
| 127 | |
| 128 base::hash_map<TaskId, base::CancellationFlag*> task_flags_; | |
| 129 | |
| 130 TaskId next_id_; | |
| 131 base::ThreadChecker thread_checker_; | |
| 132 | |
| 133 base::WeakPtrFactory<CancelableTaskTracker> weak_factory_; | |
| 134 | |
| 135 DISALLOW_COPY_AND_ASSIGN(CancelableTaskTracker); | |
| 136 }; | |
| 137 | |
| 138 } // namespace base | |
| 139 | |
| 140 #endif // BASE_TASK_CANCELABLE_TASK_TRACKER_H_ | |
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