Question

For testing an existing application I wrote a dll that can be loaded into our simulation application. All is working just fine until I want to reset the existing application from within the dll. Although the main() is restarted, it seems that the memory is not reset/initialized.
The goal is to change as little as possible in the existing application, so actually I don’t want to rewrite the application to initialize its variables at startup. Besides that, all local static variables also keep their old values.

Below a sample of how I call the existing application from within the dll.

void TimerThread::Run(void)
{
  while(true)
  {
    if ((nullptr != mpMainThread) && (mpMainThread->ThreadState == System::Threading::ThreadState::Stopped))
    {
      // Cleanup MainThread when thread has stopped
      delete mpMainThread;
      mpMainThread = nullptr;
    }

    if (nullptr == mpMainThread)
    {
      // (Re)create MainThread in which the existing application is executed
      mpMainThread = gcnew System::Threading::Thread(gcnew System::Threading::ThreadStart(&Main));
      mpMainThread->Priority = System::Threading::ThreadPriority::Highest;
      mpMainThread->Start();
    }
    dtStartTime = System::DateTime::Now;           // Keep track when started.
    if (nullptr != mpMainThread)
    {
      //Simulate timertick in existing application
      main_callback_timer_elapsed();
    }

    dtEndTime = System::DateTime::Now;
    iDuration = dtEndTime->Millisecond - dtStartTime->Millisecond;  // Determine execution time.
    System::Threading::Thread::Sleep(((TIMER_INTERVAL - iDuration) > 0) ? (miInterval - iDuration) : 0);    // Set sleep time depending on time spent
  }
}

void TimerThread::Main(void)
{
  main();     // Run main off existing application
}

void TimerThread::Reset(void)
{
  mpMainThread->Abort();      // Reset existing application by aborting MainThread
}

The main of the existing application is quite common. Below an indication of the main().

int main(void)
{
  static char test = 0;

  init_stuff();

  while(true)
  {
    test = 1;

    do_stuff();
    while(!timer_tick)
    {
      check_timer();
    }
    timer_tick = FALSE;
  }
}

The static test variable is initialized at 0 and set to 1 in the infinite loop. When the application is reset from within the dll, the main restarts, but the test variable keeps the value 1. Obviously I want this variable to be reset to 0 when I reset the application.

Any ideas?

Answer 1

If the native DLL doesn’t provide a function to reset its state then you will have to unload the DLL and then reload it. If you are using implicit linking that’s not possible. You have to use explicit linking: LoadLibrary, GetProcAddress etc.

I’m assuming that the native code is contained in a separate DLL. If that’s not the case then you are completely stuck.