opencv VideoCapture is blocked in thread - c++

Question

I need some some help with the usage of opencv VideoCapture in another thread.
When I use the VideoCapture in the main thread, it is perfectly fine and it shows the video smoothly. But once I put the code in another thread and expect it do the same thing, it seems the VideoCapture does not work at all.
I made some attempts: if I initialize the VideoCapture with 0 (the default one) as parameter, it gets blocked. But if I don't initialize it
VideoCapture cap;
or use another number
VideoCapture cap(1);
it prints out error message and exits but does not get blocked.
Here is the code:
#include <iostream>
#include <thread>
#include <functional>
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
using namespace std;
using namespace cv;
class MyClass {
public:
// display the video
static void display(int i) {
VideoCapture cap(0);
if (!cap.isOpened()) {
cout << "cannot access webcame" << endl;
exit(-1);
}
Mat imgOriginal;
namedWindow("Original", WINDOW_AUTOSIZE);
while (true) {
bool success = cap.read(imgOriginal);
if (!success) {
cout << "fail to read video into mat" << endl;
break;
}
imshow("Original", imgOriginal);
if (waitKey(30) == 27) {
break;
}
}
}
};
int main()
{
//cout << "Hello World!" << endl;
thread myThread(bind(MyClass::display, 0));
myThread.join();
return 0;
}
Very appreciated if anyone can point out where I got it wrong. Thank you.