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  1. #include <iostream>
  2. #include <string>
  3. #include <thread>
  4. #include <mutex>
  5. #include <condition_variable>
  6.  
  7. std::mutex m;
  8. std::condition_variable cv;
  9. std::string data;
  10. bool ready = false;
  11. bool processed = false;
  12.  
  13. void worker_thread()
  14. {
  15.     // Wait until main() sends data
  16.     std::unique_lock<std::mutex> lk(m, std::defer_lock);
  17.     cv.wait(lk, []{return ready;});
  18.  
  19.     // after the wait, we own the lock.
  20.     std::cout << "Worker thread is processing data\n";
  21.     data += " after processing";
  22.  
  23.     // Send data back to main()
  24.     processed = true;
  25.     std::cout << "Worker thread signals data processing completed\n";
  26.  
  27.     // Manual unlocking is done before notifying, to avoid waking up
  28.     // the waiting thread only to block again (see notify_one for details)
  29.     lk.unlock();
  30.     cv.notify_one();
  31. }
  32.  
  33. int main()
  34. {
  35.     std::thread worker(worker_thread);
  36.     std::this_thread::sleep_for(std::chrono::seconds(1));
  37.  
  38.     data = "Example data";
  39.     // send data to the worker thread
  40.     {
  41.         std::lock_guard<std::mutex> lk(m);
  42.         ready = true;
  43.         std::cout << "main() signals data ready for processing\n";
  44.     }
  45.     cv.notify_one();
  46.  
  47.     // wait for the worker
  48.     {
  49.         std::unique_lock<std::mutex> lk(m);
  50.         cv.wait(lk, []{return processed;});
  51.     }
  52.     std::cout << "Back in main(), data = " << data << '\n';
  53.  
  54.     worker.join();
  55. }
Runtime error #stdin #stdout #stderr 0s 12680KB
comments (?)
stdin
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Standard input is empty
stdout
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main() signals data ready for processing
Worker thread is processing data
Worker thread signals data processing completed
stderr
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terminate called after throwing an instance of 'std::system_error'
  what():  Operation not permitted
https://ideone.com/egjzjJ
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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