142 lines
4.9 KiB
C++
142 lines
4.9 KiB
C++
// Copyright 2014 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// CancelableTaskTracker posts tasks (in the form of a Closure) to a
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// TaskRunner, and is able to cancel the task later if it's not needed
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// anymore. On destruction, CancelableTaskTracker will cancel all
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// tracked tasks.
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//
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// Each cancelable task can be associated with a reply (also a Closure). After
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// the task is run on the TaskRunner, |reply| will be posted back to
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// originating TaskRunner.
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//
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// NOTE:
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//
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// CancelableCallback (base/cancelable_callback.h) and WeakPtr binding are
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// preferred solutions for canceling a task. However, they don't support
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// cancelation from another thread. This is sometimes a performance critical
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// requirement. E.g. We need to cancel database lookup task on DB thread when
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// user changes inputed text. If it is performance critical to do a best effort
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// cancelation of a task, then CancelableTaskTracker is appropriate,
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// otherwise use one of the other mechanisms.
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//
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// THREAD-SAFETY:
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//
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// 1. CancelableTaskTracker objects are not thread safe. They must
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// be created, used, and destroyed on the originating thread that posts the
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// task. It's safe to destroy a CancelableTaskTracker while there
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// are outstanding tasks. This is commonly used to cancel all outstanding
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// tasks.
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//
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// 2. Both task and reply are deleted on the originating thread.
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//
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// 3. IsCanceledCallback is thread safe and can be run or deleted on any
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// thread.
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#ifndef BASE_TASK_CANCELABLE_TASK_TRACKER_H_
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#define BASE_TASK_CANCELABLE_TASK_TRACKER_H_
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#include <stdint.h>
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#include "base/base_export.h"
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#include "base/callback.h"
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#include "base/containers/hash_tables.h"
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#include "base/macros.h"
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#include "base/memory/weak_ptr.h"
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#include "base/task_runner_util.h"
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#include "base/threading/thread_checker.h"
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namespace tracked_objects {
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class Location;
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} // namespace tracked_objects
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namespace base {
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class CancellationFlag;
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class TaskRunner;
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class BASE_EXPORT CancelableTaskTracker {
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public:
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// All values except kBadTaskId are valid.
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typedef int64_t TaskId;
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static const TaskId kBadTaskId;
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typedef base::Callback<bool()> IsCanceledCallback;
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CancelableTaskTracker();
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// Cancels all tracked tasks.
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~CancelableTaskTracker();
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TaskId PostTask(base::TaskRunner* task_runner,
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const tracked_objects::Location& from_here,
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const base::Closure& task);
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TaskId PostTaskAndReply(base::TaskRunner* task_runner,
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const tracked_objects::Location& from_here,
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const base::Closure& task,
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const base::Closure& reply);
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template <typename TaskReturnType, typename ReplyArgType>
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TaskId PostTaskAndReplyWithResult(
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base::TaskRunner* task_runner,
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const tracked_objects::Location& from_here,
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const base::Callback<TaskReturnType(void)>& task,
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const base::Callback<void(ReplyArgType)>& reply) {
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TaskReturnType* result = new TaskReturnType();
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return PostTaskAndReply(
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task_runner,
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from_here,
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base::Bind(&base::internal::ReturnAsParamAdapter<TaskReturnType>,
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task,
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base::Unretained(result)),
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base::Bind(&base::internal::ReplyAdapter<TaskReturnType, ReplyArgType>,
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reply,
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base::Owned(result)));
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}
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// Creates a tracked TaskId and an associated IsCanceledCallback. Client can
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// later call TryCancel() with the returned TaskId, and run |is_canceled_cb|
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// from any thread to check whether the TaskId is canceled.
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//
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// The returned task ID is tracked until the last copy of
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// |is_canceled_cb| is destroyed.
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//
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// Note. This function is used to address some special cancelation requirement
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// in existing code. You SHOULD NOT need this function in new code.
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TaskId NewTrackedTaskId(IsCanceledCallback* is_canceled_cb);
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// After calling this function, |task| and |reply| will not run. If the
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// cancelation happens when |task| is running or has finished running, |reply|
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// will not run. If |reply| is running or has finished running, cancellation
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// is a noop.
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//
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// Note. It's OK to cancel a |task| for more than once. The later calls are
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// noops.
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void TryCancel(TaskId id);
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// It's OK to call this function for more than once. The later calls are
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// noops.
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void TryCancelAll();
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// Returns true iff there are in-flight tasks that are still being
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// tracked.
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bool HasTrackedTasks() const;
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private:
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void Track(TaskId id, base::CancellationFlag* flag);
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void Untrack(TaskId id);
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base::hash_map<TaskId, base::CancellationFlag*> task_flags_;
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TaskId next_id_;
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base::ThreadChecker thread_checker_;
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base::WeakPtrFactory<CancelableTaskTracker> weak_factory_;
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DISALLOW_COPY_AND_ASSIGN(CancelableTaskTracker);
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};
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} // namespace base
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#endif // BASE_TASK_CANCELABLE_TASK_TRACKER_H_
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