title: qt blocking connection deadlock
body: <p>In my code a worker thread emits a signal.</p>
  
  <p>From <a href="http://qt-project.org/doc/qt-4.8/qt.html#ConnectionType-enum" rel="nofollow">Qt Docs</a>:</p>
  
  <blockquote>
    <p>Qt::BlockingQueuedConnection   -   Same as QueuedConnection, except the current thread blocks until the slot returns. This connection type should only be used where the emitter and receiver are in different threads. <em>Note:</em> Violating this rule can cause your application to deadlock.</p>
  </blockquote>
  
  <p>How to determine when emitter and receiver are in different threads. I have some vague ideas about that, because I had problems with my application till I added <code>Qt::BlockingQueuedConnection</code> flag. But know my application does not want to close. It is stuck with working thread.</p>
  
  <p><strong>UPDATE:</strong></p>
  
  <p>I investigate the problem more. The thread is blocked by emitted signals. Because when I close the application, the slots (in MainWindow) are destroyed, and emit signal produce this deadlock.</p>
  
  <p>How to solve this issue?</p>