#include <QtConcurrent>
#include <QApplication>
#include <QFutureWatcher>

#include <iostream>

struct Guard
{
  Guard() {}

  ~Guard()
  {
    std::cout << "I enter here multiple times" << std::endl;
    QtConcurrent::run([]()
    {
      std::cout << "But here once, or never" << std::endl;
    });
  }
};


Guard guard()
{
  return Guard{};
}


int main(int argc, char** argv)
{
  QApplication app(argc, argv);

  QFuture<Guard> future = QtConcurrent::run(guard);
  auto* watcher = new QFutureWatcher<Guard>();
  {
    auto g = guard();
  }
  QObject::connect(watcher, &QFutureWatcher<Guard>::finished, &app, [future]()
  {
    auto guard = future.result();
  });
  watcher->setFuture(future);

  app.exec();
}