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TMessagesProj/jni/voip/webrtc/base/task/cancelable_task_tracker.h

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+// 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 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:
+//
+// CancelableCallback (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 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. 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/bind.h"
+#include "base/callback.h"
+#include "base/callback_helpers.h"
+#include "base/containers/small_map.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "base/post_task_and_reply_with_result_internal.h"
+#include "base/sequence_checker.h"
+#include "base/synchronization/atomic_flag.h"
+
+namespace base {
+
+class Location;
+class ScopedClosureRunner;
+class TaskRunner;
+
+class BASE_EXPORT CancelableTaskTracker {
+ public:
+  // All values except kBadTaskId are valid.
+  typedef int64_t TaskId;
+  static const TaskId kBadTaskId;
+
+  using IsCanceledCallback = RepeatingCallback<bool()>;
+
+  CancelableTaskTracker();
+
+  // Cancels all tracked tasks.
+  ~CancelableTaskTracker();
+
+  TaskId PostTask(TaskRunner* task_runner,
+                  const Location& from_here,
+                  OnceClosure task);
+
+  TaskId PostTaskAndReply(TaskRunner* task_runner,
+                          const Location& from_here,
+                          OnceClosure task,
+                          OnceClosure reply);
+
+  template <typename TaskReturnType, typename ReplyArgType>
+  TaskId PostTaskAndReplyWithResult(TaskRunner* task_runner,
+                                    const Location& from_here,
+                                    OnceCallback<TaskReturnType()> task,
+                                    OnceCallback<void(ReplyArgType)> reply) {
+    auto* result = new std::unique_ptr<TaskReturnType>();
+    return PostTaskAndReply(
+        task_runner, from_here,
+        BindOnce(&internal::ReturnAsParamAdapter<TaskReturnType>,
+                 std::move(task), Unretained(result)),
+        BindOnce(&internal::ReplyAdapter<TaskReturnType, ReplyArgType>,
+                 std::move(reply), Owned(result)));
+  }
+
+  // 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:
+  // Cancellation flags are ref-counted to ensure they remain valid even if the
+  // tracker and its calling thread are torn down while there are still
+  // cancelable tasks queued to the target TaskRunner.
+  // See https://crbug.com/918948.
+  using TaskCancellationFlag = RefCountedData<AtomicFlag>;
+
+  static void RunIfNotCanceled(
+      const scoped_refptr<SequencedTaskRunner>& origin_task_runner,
+      const scoped_refptr<TaskCancellationFlag>& flag,
+      OnceClosure task);
+  static void RunThenUntrackIfNotCanceled(
+      const scoped_refptr<SequencedTaskRunner>& origin_task_runner,
+      const scoped_refptr<TaskCancellationFlag>& flag,
+      OnceClosure task,
+      OnceClosure untrack);
+  static bool IsCanceled(
+      const scoped_refptr<SequencedTaskRunner>& origin_task_runner,
+      const scoped_refptr<TaskCancellationFlag>& flag,
+      const ScopedClosureRunner& cleanup_runner);
+
+  void Track(TaskId id, scoped_refptr<TaskCancellationFlag> flag);
+  void Untrack(TaskId id);
+
+  // Typically the number of tasks are 0-2 and occationally 3-4. But since
+  // this is a general API that could be used in unexpected ways, use a
+  // small_map instead of a flat_map to avoid falling over if there are many
+  // tasks.
+  small_map<std::map<TaskId, scoped_refptr<TaskCancellationFlag>>, 4>
+      task_flags_;
+
+  TaskId next_id_ = 1;
+  SequenceChecker sequence_checker_;
+
+  // TODO(https://crbug.com/1009795): Remove once crasher is resolved.
+  base::WeakPtr<CancelableTaskTracker> weak_this_;
+  base::WeakPtrFactory<CancelableTaskTracker> weak_factory_{this};
+
+  DISALLOW_COPY_AND_ASSIGN(CancelableTaskTracker);
+};
+
+}  // namespace base
+
+#endif  // BASE_TASK_CANCELABLE_TASK_TRACKER_H_