#include <iostream>
#include <string>
#include <thread>
#include <mutex>
#include <condition_variable>

std::mutex mtx;
std::condition_variable cv;
std::string data;
bool ready = false;
bool processed = false;

void worker_thread() {
    
    std::unique_lock<std::mutex> ulk(mtx);

    // wait中的谓词返回false为虚假唤醒，继续阻塞；为true，则真实唤醒
    cv.wait(ulk, []{ return ready;});

    // 占有锁
    std::cout << "Worker thread is processing data\n";
    data += " after processing";

    // 处理完成
    processed = true;
    std::cout << "Worker thread signals data processing complated\n";

    // 通知前完成手动解锁，以避免主线程才被唤醒就阻塞
    ulk.unlock();
    cv.notify_one(); 
}

int main() {
    std::thread worker(worker_thread);

    data = "Example data";
    // 发送数据到 worker 线程
    {
        std::lock_guard<std::mutex> ulk(mtx);
        ready = true;
        std::cout << "main() signals data ready for processing\n";
    }
    cv.notify_one();

    // 等候 worker
    {
        std::unique_lock<std::mutex> ulk(mtx);
        cv.wait(ulk, []{ return processed;});
    }
    std::cout << "Back in main() , data = " << data << '\n';

    worker.join();
}