[OpenCV] multithread capture

#include "barter.h"
#include "fps_stats.hpp"
#include <opencv2/opencv.hpp>
#include <string>
#include <list>
#include <thread>

enum ThreadState {
    Pause, Running, Quit
};

//std::list<cv::Mat> frames;
cv::VideoCapture cap;
barter<cv::Mat> frame_barter;
std::atomic_int t_state{ ThreadState::Pause };

// thread function for video getting and show
void StreamThread(barter<cv::Mat>& frame_barter_, std::atomic_int& t_state_)
{
    auto frame = std::unique_ptr<cv::Mat>(new cv::Mat);
    for (;;) {
        // wait for a new frame to arrive
        while (t_state_ != ThreadState::Running) {
            if (t_state_ == ThreadState::Quit) return;
            std::this_thread::sleep_for(std::chrono::microseconds(30));
        }
        frame_barter_.exchange(frame);
        CV_Assert(frame);

        if (frame->empty()) continue;
        //cv::imshow("R1", *frame);
        //cv::waitKey(1);
    }
}


int main(int, char)
{
    cap.open(0);

    //open check
    if (!cap.isOpened()) {
        std::cerr << "Stream open failed : " << std::endl;
        return 1;
    }

    cv::setNumThreads(8);


    std::thread t1{ &StreamThread, std::ref(frame_barter), std::ref(t_state) };

    auto frame = std::unique_ptr<cv::Mat>(new cv::Mat);
    std::this_thread::sleep_for(std::chrono::seconds(1));
    std::cout << "cv::getNumThreads(): " << cv::getNumThreads() << std::endl;

    fps_stats fps{ "Video" };
    cap >> *frame;
    while (!frame->empty())
    {
        cv::imshow("Result", *frame);

        frame_barter.exchange(frame);
        t_state = ThreadState::Running;

        if (cv::waitKey(1) >= 0)
        {
            break;
        }
        cap >> *frame;
        fps.tick();
    }

    if (t1.joinable())
    {
        t_state = ThreadState::Quit;
        t1.join();
        std::cout << "t1 is joined" << std::endl;
    }

    return 0;
}