helgrind/tests/bug392331.cpp

   1 // For this Bugzilla item https://bugs.kde.org/show_bug.cgi?id=392331
   2 // Example from https://en.cppreference.com/w/cpp/thread/condition_variable
   3
   4 #include <iostream>
   5 #include <string>
   6 #include <thread>
   7 #include <mutex>
   8 #include <condition_variable>
   9
  10 std::mutex m;
  11 std::condition_variable cv;
  12 std::string data;
  13 bool ready = false;
  14 bool processed = false;
  15
  16 void worker_thread()
  17 {
  18     // Wait until main() sends data
  19     std::unique_lock lk(m);
  20     cv.wait(lk, []{return ready;});
  21
  22     // after the wait, we own the lock.
  23     std::cout << "Worker thread is processing data\n";
  24     data += " after processing";
  25
  26     // Send data back to main()
  27     processed = true;
  28     std::cout << "Worker thread signals data processing completed\n";
  29
  30     // Manual unlocking is done before notifying, to avoid waking up
  31     // the waiting thread only to block again (see notify_one for details)
  32     lk.unlock();
  33     cv.notify_one();
  34 }
  35
  36 int main()
  37 {
  38     std::thread worker(worker_thread);
  39
  40     data = "Example data";
  41     // send data to the worker thread
  42     {
  43         std::lock_guard lk(m);
  44         ready = true;
  45         std::cout << "main() signals data ready for processing\n";
  46     }
  47     cv.notify_one();
  48
  49     // wait for the worker
  50     {
  51         std::unique_lock lk(m);
  52         cv.wait(lk, []{return processed;});
  53     }
  54     std::cout << "Back in main(), data = " << data << '\n';
  55
  56     worker.join();
  57 }
  58