如何确保在notify_one之前调用wait_for

条件变量的典型用法如下所示（请参阅下面的代码）： http://en.cppreference.com/w/cpp/thread/condition_variable。

但是，似乎主线程可能会在工作线程调用wait之前调用notify_one，这将导致死锁。我弄错了吗？如果没有，通常的解决方法是什么？

#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()
{
    // Wait until main() sends data
    std::unique_lock<std::mutex> lk(m);
    cv.wait(lk, []{return ready;});
    // after the wait, we own the lock.
    std::cout << "Worker thread is processing datan";
    data += " after processing";
    // Send data back to main()
    processed = true;
    std::cout << "Worker thread signals data processing completedn";
    // Manual unlocking is done before notifying, to avoid waking up
    // the waiting thread only to block again (see notify_one for details)
    lk.unlock();
    cv.notify_one();
}
int main()
{
    std::thread worker(worker_thread);
    data = "Example data";
    // send data to the worker thread
    {
        std::lock_guard<std::mutex> lk(m);
        ready = true;
        std::cout << "main() signals data ready for processingn";
    }
    cv.notify_one();
    // wait for the worker
    {
        std::unique_lock<std::mutex> lk(m);
        cv.wait(lk, []{return processed;});
    }
    std::cout << "Back in main(), data = " << data << 'n';
    worker.join();
}