c++如何使用条件变量std::condition_variable_c++线程同步条件变量用法

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

std::queue<int> data_queue;
std::mutex mtx;
std::condition_variable cv;
bool finished = false;

void producer() {
    for (int i = 0; i < 5; ++i) {
        std::this_thread::sleep_for(std::chrono::milliseconds(100));
        std::unique_lock<std::mutex> lock(mtx);
        data_queue.push(i);
        std::cout << "Produced: " << i << '\n';
        lock.unlock();
        cv.notify_one(); // 唤醒一个等待的消费者
    }

    {
        std::unique_lock<std::mutex> lock(mtx);
        finished = true;
    }
    cv.notify_all(); // 通知所有消费者结束
}

void consumer() {
    while (true) {
        std::unique_lock<std::mutex> lock(mtx);

        // 条件等待：队列非空 或 生产结束
        cv.wait(lock, [] { 
            return !data_queue.empty() || finished; 
        });

        if (!data_queue.empty()) {
            int value = data_queue.front();
            data_queue.pop();
            std::cout << "Consumed: " << value << '\n';
        }

        if (data_queue.empty() && finished) {
            break;
        }

        lock.unlock();
    }
    std::cout << "Consumer exiting.\n";
}

int main() {
    std::thread p(producer);
    std::thread c(consumer);

    p.join();
    c.join();

    return 0;
}

while (!predicate()) {
    cv.wait(lock);
}

while (data_queue.empty() && !finished) {
    cv.wait(lock);
}