请问C++跨平台应该如何更好的获取线程id并维护线程id到实例指针的映射？

#include<iostream>
#include <unordered_map>
#include<thread>

class MyClass {
public:
    MyClass() {
        thread_id = std::this_thread::get_id();
        instances[thread_id] = this;
    }

    ~MyClass() {
        instances.erase(thread_id);
    }

    static MyClass* getInstance(std::thread::id id) {
        return instances[id];
    }

private:
    std::thread::id thread_id;
    static std::unordered_map<std::thread::id, MyClass*> instances;
};

std::unordered_map<std::thread::id, MyClass*> MyClass::instances;

void thread_func() {
    MyClass* instance = MyClass::getInstance(std::this_thread::get_id());
    std::cout << "Thread ID: "<< std::this_thread::get_id() << ", Instance pointer: "<< instance<< std::endl;
}

int main() {
    std::thread t1(thread_func);
    std::thread t2(thread_func);

    t1.join();
    t2.join();

    return 0;
}