axmol/core/base/CCAsyncTaskPool.h

/****************************************************************************
Copyright (c) 2013-2016 Chukong Technologies Inc.
Copyright (c) 2017-2018 Xiamen Yaji Software Co., Ltd.

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#ifndef __CCSYNC_TASK_POOL_H_
#define __CCSYNC_TASK_POOL_H_

#include "platform/CCPlatformMacros.h"
#include "base/CCDirector.h"
#include "base/CCScheduler.h"
#include <vector>
#include <queue>
#include <memory>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <future>
#include <functional>
#include <stdexcept>

/**
 * @addtogroup base
 * @{
 */
NS_CC_BEGIN

/**
 * @class AsyncTaskPool
 * @brief This class allows to perform background operations without having to manipulate threads.
 * @js NA
 */
class CC_DLL AsyncTaskPool
{
public:
    typedef std::function<void(void*)> TaskCallBack;

    enum class TaskType
    {
        TASK_IO,
        TASK_NETWORK,
        TASK_OTHER,
        TASK_MAX_TYPE,
    };

    /**
     * Returns the shared instance of the async task pool.
     */
    static AsyncTaskPool* getInstance();

    /**
     * Destroys the async task pool.
     */
    static void destroyInstance();

    /**
     * Stop tasks.
     *
     * @param type Task type you want to stop.
     */
    void stopTasks(TaskType type);

    /**
     * Enqueue a asynchronous task.
     *
     * @param type task type is io task, network task or others, each type of task has a thread to deal with it.
     * @param callback callback when the task is finished. The callback is called in the main thread instead of task
     * thread.
     * @param callbackParam parameter used by the callback.
     * @param task: task can be lambda function to be performed off thread.
     * @lua NA
     */
    void enqueue(TaskType type, TaskCallBack callback, void* callbackParam, std::function<void()> task);

    /**
     * Enqueue a asynchronous task.
     *
     * @param type task type is io task, network task or others, each type of task has a thread to deal with it.
     * @param task: task can be lambda function to be performed off thread.
     * @lua NA
     */
    void enqueue(AsyncTaskPool::TaskType type, std::function<void()> task);

    AsyncTaskPool();
    ~AsyncTaskPool();

protected:
    // thread tasks internally used
    class ThreadTasks
    {
        struct AsyncTaskCallBack
        {
            TaskCallBack callback;
            void* callbackParam;
        };

    public:
        ThreadTasks() : _stop(false)
        {
            _thread = std::thread([this] {
                for (;;)
                {
                    std::function<void()> task;
                    AsyncTaskCallBack callback;
                    {
                        std::unique_lock<std::mutex> lock(this->_queueMutex);
                        this->_condition.wait(lock, [this] { return this->_stop || !this->_tasks.empty(); });
                        if (this->_stop && this->_tasks.empty())
                            return;
                        task     = std::move(this->_tasks.front());
                        callback = std::move(this->_taskCallBacks.front());
                        this->_tasks.pop();
                        this->_taskCallBacks.pop();
                    }

                    task();
                    Director::getInstance()->getScheduler()->performFunctionInCocosThread(
                        std::bind(callback.callback, callback.callbackParam));
                }
            });
        }
        ~ThreadTasks()
        {
            {
                std::unique_lock<std::mutex> lock(_queueMutex);
                _stop = true;

                while (_tasks.size())
                    _tasks.pop();
                while (_taskCallBacks.size())
                    _taskCallBacks.pop();
            }
            _condition.notify_all();
            _thread.join();
        }
        void clear()
        {
            std::unique_lock<std::mutex> lock(_queueMutex);
            while (_tasks.size())
                _tasks.pop();
            while (_taskCallBacks.size())
                _taskCallBacks.pop();
        }

        void enqueue(TaskCallBack callback, void* callbackParam, std::function<void()> task)
        {
            AsyncTaskCallBack taskCallBack;
            taskCallBack.callback      = std::move(callback);
            taskCallBack.callbackParam = callbackParam;

            {
                std::unique_lock<std::mutex> lock(_queueMutex);

                // don't allow enqueueing after stopping the pool
                if (_stop)
                {
                    CC_ASSERT(0 && "already stop");
                    return;
                }

                _tasks.push(std::move(task));
                _taskCallBacks.push(std::move(taskCallBack));
            }
            _condition.notify_one();
        }

    private:
        // need to keep track of thread so we can join them
        std::thread _thread;
        // the task queue
        std::queue<std::function<void()>> _tasks;
        std::queue<AsyncTaskCallBack> _taskCallBacks;

        // synchronization
        std::mutex _queueMutex;
        std::condition_variable _condition;
        bool _stop;
    };

    // tasks
    ThreadTasks _threadTasks[int(TaskType::TASK_MAX_TYPE)];

    static AsyncTaskPool* s_asyncTaskPool;
};

inline void AsyncTaskPool::stopTasks(TaskType type)
{
    auto& threadTask = _threadTasks[(int)type];
    threadTask.clear();
}

inline void AsyncTaskPool::enqueue(AsyncTaskPool::TaskType type,
                                   TaskCallBack callback,
                                   void* callbackParam,
                                   std::function<void()> task)
{
    auto& threadTask = _threadTasks[(int)type];

    threadTask.enqueue(std::move(callback), callbackParam, std::move(task));
}

inline void AsyncTaskPool::enqueue(AsyncTaskPool::TaskType type, std::function<void()> task)
{
    enqueue(
        type, [](void*) {}, nullptr, std::move(task));
}

NS_CC_END
// end group
/// @}
#endif  //__CCSYNC_TASK_POOL_H_