c++ 条件变量

清疚 2023-06-06 04:53 22阅读 0赞

//
    // Created by wuyongyu on 2019-10-10.
    //
    
    #include <iostream>
    #include <string>
    #include <thread>
    #include <mutex>
    #include <chrono>
    #include <condition_variable>
    
    using namespace std::chrono_literals; // for sleep_for(10s)
    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);
      std::cout << "work_thread id:" << std::this_thread::get_id() << std::endl;
      // condition_vadiable will block this thread
       cv.wait(lk, []{
         std::cout << "wait ready:" << ready << std::endl;
         return ready;});
    
      // after the wait, we own the lock.
      std::cout << "Worker thread is processing data\n";
      data += " after processing";
    
      // Send data back to main()
      processed = true;
      std::cout << "Worker thread signals data processing completed\n";
    
      // Manual unlocking is done before notifying, to avoid waking up
      // the waiting thread only to block again (see notify_one for details)
      lk.unlock();
      // sleep 5s ,then notify the thread
      std::this_thread::sleep_for(5s);
      cv.notify_one();
    }
    
    int main()
    {
    
      data = "Example data";
      // send data to the worker thread
      {
        // std::lock_guard<std::mutex> lk(m);
        std::unique_lock<std::mutex> lock(m);
        ready = true;
        std::cout << "main() signals data ready for processing\n";
        lock.unlock();
      }
      std::thread worker(worker_thread);
    
      // sleep 5s ,then notify the thread
      std::this_thread::sleep_for(5s);
      cv.notify_one();
      // wait for the worker
      {
        std::unique_lock<std::mutex> lk(m);
        cv.wait(lk, []{return processed;});
        std::cout << "main() get process " << std::endl;
        lk.unlock();
      }
      std::cout << "Back in main(), data = " << data << '\n';
      worker.join();
      return 0;
    }