title: Qt's default threads
body: <p>When I start a new Qt application with a minimal amount of code and run it, I see that there are a number of threads running, which at a minimum is 2 and can be as many as 5. It usually settles at 2, until I drag the window around, at which time I see up to 4 threads running.</p>
  
  <p>This is all the code I'm using: -</p>
  
  <pre><code>#include &lt;QApplication&gt;
  #include &lt;QWidget&gt;
  
  int main(int argc, char *argv[])
  {
      QApplication a(argc, argv);
  
      QWidget mainWindow;
      mainWindow.show();
  
      return a.exec();
  }
  </code></pre>
  
  <p>Can someone explain why there are different threads and what they're likely to be for? Originally I expected just one, but wouldn't be surprised if a second was used for handling messages. However, what could account for the other threads?</p>