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// Copyright 2016 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef COMPONENTS_OFFLINE_PAGES_TASK_TASK_QUEUE_H_
#define COMPONENTS_OFFLINE_PAGES_TASK_TASK_QUEUE_H_
#include <memory>
#include <vector>
#include "base/containers/circular_deque.h"
#include "base/functional/callback.h"
#include "base/location.h"
#include "base/memory/raw_ptr.h"
#include "base/memory/ref_counted.h"
#include "base/memory/weak_ptr.h"
#include "base/sequence_checker.h"
#include "components/offline_pages/task/task.h"
namespace base {
class SingleThreadTaskRunner;
} // namespace base
namespace offline_pages {
// Class for coordinating |Task|s in relation to access to a specific resource.
// As a task, we understand a set of asynchronous operations (possibly switching
// threads) that access a set of sensitive resource(s). Because the resource
// state is modified and individual steps of a task are asynchronous, allowing
// certain tasks to run in parallel may lead to incorrect results. This class
// allows for ordering of tasks in a FIFO manner, to ensure two tasks modifying
// a resources are not run at the same time.
//
// Consumers of this class should create an instance of TaskQueue and implement
// tasks that need to be run sequentially. New task will only be started when
// the previous one calls |Task::TaskComplete|.
//
// Methods on TaskQueue should be called from the same thread from which it
// is created.
class TaskQueue {
public:
class Delegate {
public:
virtual ~Delegate() = default;
// Invoked once when TaskQueue reached 0 tasks.
virtual void OnTaskQueueIsIdle() = 0;
};
explicit TaskQueue(Delegate* delegate);
TaskQueue(const TaskQueue&) = delete;
TaskQueue& operator=(const TaskQueue&) = delete;
~TaskQueue();
// Adds a task to the queue. Queue takes ownership of the task. Optionally,
// use FROM_HERE as the first parameter for debugging.
void AddTask(std::unique_ptr<Task> task);
void AddTask(const base::Location& from_here, std::unique_ptr<Task> task);
// Whether the task queue has any pending (not-running) tasks.
bool HasPendingTasks() const;
// Whether there is a task currently running.
bool HasRunningTask() const;
// Returns a human-readable string describing the contents of the task queue.
std::string GetStateForTesting() const;
private:
friend Task;
struct Entry;
// Checks whether there are any tasks to run, as well as whether no task is
// currently running. When both are met, it will start the next task in the
// queue.
void StartTaskIfAvailable();
void RunCurrentTask();
void ResumeCurrentTask(base::OnceClosure on_resume);
// Callback for informing the queue that a task was completed. Can be called
// from any thread.
static void TaskCompletedCallback(
scoped_refptr<base::SingleThreadTaskRunner> task_runner,
base::WeakPtr<TaskQueue> task_queue,
Task* task);
void SuspendTask(Task* task);
void ResumeTask(Task* task, base::OnceClosure on_resume);
void TaskCompleted(Task* task);
void InformTaskQueueIsIdle();
// This TaskQueue's task runner, set on construction using the instance
// assigned to the current thread.
scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
// Owns and outlives this TaskQueue.
raw_ptr<Delegate> delegate_;
// Currently running tasks.
std::unique_ptr<Task> current_task_;
base::Location current_task_location_;
// A FIFO queue of tasks that will be run using this task queue.
base::circular_deque<Entry> tasks_;
// A set of tasks which are suspended.
std::vector<Entry> suspended_tasks_;
SEQUENCE_CHECKER(sequence_checker_);
base::WeakPtrFactory<TaskQueue> weak_ptr_factory_{this};
};
} // namespace offline_pages
#endif // COMPONENTS_OFFLINE_PAGES_TASK_TASK_QUEUE_H_
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