C++11 多线程 问题

#include <iostream>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <future>
#include <functional>
#include <chrono>

std::mutex mt;
std::condition_variable cv;
bool _isReady = 0;
void func()
{
    std::unique_lock<std::mutex> lck(mt);
    std::cout << "func get the lock" << std::endl;
    while(!_isReady)
    {
        cv.wait(lck);
    }
    std::cout << "func lock status : " << lck.owns_lock() << std::endl;
    // lck.unlock();
    _isReady = !_isReady;
    cv.notify_all();
    // std::this_thread::yield();
    // lck.lock();
    while(!_isReady)
    {
        cv.wait(lck);
    }
    std::cout << "func get the lock the lock status : " << lck.owns_lock() << std::endl;
}
int main()
{
    std::unique_lock<std::mutex> lck(mt);
    std::cout << "main get the lock" << std::endl;
    std::thread t1(func);
    _isReady = !_isReady;
    lck.unlock();
    cv.notify_all();
    // std::this_thread::yield();
    // lck.lock();
    while(_isReady)
    {
        cv.wait(lck);
    }
    _isReady = !_isReady;
    lck.unlock();
    std::this_thread::yield();
   
    t1.join();
    return 0;
}