cocos-enhance-kit/cocos2d-x/extensions/assets-manager/CCAsyncTaskPool.h

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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 "CCPlatformDefine.h"
#include "platform/CCApplication.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 f task can be lambda function.
     * @lua NA
     */
    template<class F>
    inline void enqueue(TaskType type, const TaskCallBack& callback, void* callbackParam, F&& f);

CC_CONSTRUCTOR_ACCESS:
    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();
                                          Application::getInstance()->getScheduler()->performFunctionInCocosThread([&, callback]{ 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();
        }
        template<class F>
        void enqueue(const TaskCallBack& callback, void* callbackParam, F&& f)
        {
            auto task = f;//std::bind(std::forward<F>(f), std::forward<Args>(args)...);

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

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

                AsyncTaskCallBack taskCallBack;
                taskCallBack.callback = callback;
                taskCallBack.callbackParam = callbackParam;
                _tasks.emplace([task](){ task(); });
                _taskCallBacks.emplace(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();
}

template<class F>
inline void AsyncTaskPool::enqueue(AsyncTaskPool::TaskType type, const TaskCallBack& callback, void* callbackParam, F&& f)
{
    auto& threadTask = _threadTasks[(int)type];

    threadTask.enqueue(callback, callbackParam, f);
}


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