C++ windows 多线程 互斥锁

#include <opencv2/core/version.hpp>
#include <opencv2/calib3d/calib3d.hpp>
#include <opencv2/opencv.hpp>

using namespace System::Runtime::InteropServices;
using namespace System::IO;
using namespace System::Data;
using namespace System::Drawing;
using namespace System::Drawing::Imaging;
using namespace System::Runtime::Serialization::Formatters::Binary;
using namespace System::Windows::Forms;
using namespace System::Threading;

using namespace FRS;
using namespace FRS::Util;
using namespace DataAngine;

HANDLE hMutex = CreateMutex(NULL,FALSE,NULL);


cv::VideoCapture *cap;
void Show(){
    while (true){
        cv::Mat frame;
        WaitForSingleObject(hMutex, INFINITE);
        cap>>frame;
        ReleaseMutex(hMutex);
        imshow("video", frame);
        cv::waitKey(1000 / cap->get(CV_CAP_PROP_FPS));
    }
}
int main()
{
    FeatureData ^fa = gcnew FeatureData();

    //cap.open(0);
    cap = new cv::VideoCapture();
    cap->open("rtsp://admin:admin12345@172.18.132.234:554");

    if (!cap->isOpened())
    {
        std::cout << "open rtsp error" << std::endl;
        return 0;
    }
    Thread ^showThread = gcnew Thread(gcnew ThreadStart(Show));
    showThread->Start();
    
    bool stop = true;
    while (stop)
    {
        cv::Mat frame;
        WaitForSingleObject(hMutex, INFINITE);
        cap>>frame;
        ReleaseMutex(hMutex);
        if (frame.empty()) continue;
        System::GC::Collect();
        
        Thread::Sleep(100);
    }
}

本代码为人脸识别视频处理代码，包含两个线程，其中Show线程为opencv读取rtsp流，主线程代码自填。其中GC::Collect()为程序垃圾回收。

代码本为单线程，书写中发现VideoCapture读取视频流时存在缓存，并有缓存上限，单纯进行主线程视频处理时会因为处理时间较长发生缓存溢出问题，所以增设多线程Show()读取消耗VideoCapture缓存。

增设Show()线程时发现存在两线程同时读取缓存现象，添加互斥锁hMutex ，代码中包含互斥锁的句柄初始化以及加锁解锁代码。