条件变量 condition

wait(阻塞当前线程，直到条件变量被唤醒)

#include <iostream>

#include <string>

#include <thread>

#include <mutex>

#include <condition_variable>

std::mutex m;

std::condition_variable cv;

std::string data;

bool ready = false;

bool processed = false;

void worker_thread()

{

    // 等待直至 main() 发送数据

    std::unique_lock<std::mutex> lk(m);

    cv.wait(lk, []{return ready;});

    // 等待后，我们占有锁。

    std::cout << "Worker thread is processing data\n";

    data += " after processing";

    // 发送数据回 main()

    processed = true;

    std::cout << "Worker thread signals data processing completed\n";

    // 通知前完成手动解锁，以避免等待线程才被唤醒就阻塞（细节见 notify_one ）

    lk.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> lk(m);

        ready = true;

        std::cout << "main() signals data ready for processing\n";

    }

    cv.notify_one();

    // 等候 worker

    {

        std::unique_lock<std::mutex> lk(m);

        cv.wait(lk, []{return processed;});

    }

    std::cout << "Back in main(), data = " << data << '\n';

    worker.join();

}

巴特西

条件变量 condition_variable wait

wait(阻塞当前线程，直到条件变量被唤醒)

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