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();
}