Hello guys I'm learning Qt and I've reached QThread class. Having no experience in multithreading I spent several hours studying semaphores, mutexes, critical sections and wait functions in Win32API. When I launched several threads there and ++ and -- a global variable without synchronization I got different results each time. Now I am trying to do the same with QThread but I am getting failed. Can you tell me what's wrong? here is my code:
Qt Code: 
  1. #include <QCoreApplication>
  2. #include <QMutex>
  3. #include <QThread>
  4. #include <cstdio>
  5.  
  6. static const int N = 2000000;
  7.  
  8. class Thread : public QThread {
  9. public:
  10.     Thread();
  11.     void run();
  12. private:
  13.     void Inc();
  14.     void Dec();
  15.     static QMutex mutex;
  16. };
  17.  
  18. QMutex Thread::mutex;
  19. static int g_counter = 0;
  20.  
  21. int main(int argc, char *argv[]) {
  22.     QCoreApplication app(argc, argv);
  23.     Thread A, B, C;
  24.     A.run();
  25.     B.run();
  26.     C.run();
  27.     char c;
  28.     scanf("%c", &c);
  29.     printf("%d\n", g_counter);
  30.     return app.exec();
  31. }
  32.  
  33. Thread::Thread() {
  34.  
  35. }
  36.  
  37. void Thread::run() {
  38.     //QMutexLocker lock(&mutex);
  39.     for (int i = 0; i < N; ++i) {
  40.         ++g_counter;
  41.         --g_counter;
  42.     }
  43. }
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