[QUESTION] Something confusing when I import the library from a std::thread in c++

[z-pc]

I want to call some functions in Python by C++ program. This is my sample:
"testmain.cpp"

// Example program
#include <iostream>
#include <fstream>
#include <utility>
#include <thread>
#include "pybind11/embed.h"
#include "pybind11/stl.h"

namespace py = pybind11;

static void TestThread(const char* path)
{
	py::module_ sys__ = py::module_::import("sys");
	std::cout << "import sys success" << std::endl;
	py::module_ cv2 = py::module_::import("cv2"); //-> 1. This line confuses me
	std::cout << "preparing imread" << std::endl;
	cv2.attr("imread")(path);
	std::cout << "imread success" << std::endl;
}

int main(int argc, const char** argv) 
{
	pybind11::scoped_interpreter guard{};
	{
		try
		{
			//py::module_::import("cv2");  //-> 2. This line confuses me
			std::string path("G:/ocr6DD1.tmp");
			std::thread th(TestThread, path.c_str());

			if (th.joinable())
				th.join();
		}
		catch (const pybind11::error_already_set& e)
		{
			std::cout << e.what() << std::endl;
		}
		catch (const std::exception& e)
		{
			std::cout << e.what() << std::endl;
		}
		catch (const std::runtime_error& e)
		{
			std::cout << e.what() << std::endl;
		}

	}
	return 1;
}

In my local, when running the thread to this line

py::module_ cv2 = py::module_::import("cv2"); //-> 1. This line confuses me

The program is suspended indefinitely, but If I uncomment this line

//py::module_::import("cv2");  //-> 2. This line confuses me

the thread will passing that import opencv.
I'm just learning about pybind11 and the interpreter, looking forward to a detailed answer.

Information:
Win10 x64
Visual Studio 2019 Enterprise
Opencv-python 4.5.2.54

[z-pc]

I found an answer in this #1273