title: QtConcurrent.run() with a c++11 lambda that captures a reference to "this" to emit signal
body: <p>While this works, I have this strange feeling my QObject emit is not threadsafe and the fact that this hasn't exploded yet is just luck.</p>
  
  <pre><code>void LoginController::attemptLogin(QString username, QString password)
  {
      emit loginAttemptStatus(QString("Connecting to service..."));
      QFuture&lt;bool&gt; future = QtConcurrent::run([&amp;](QString username, QString password){
              // fake a long running operation
              QThread::sleep(1);
              emit loginAttemptStatus(QString("Connected to service..."));
              // a dumb test login
              QString u("asdf");
              bool success = username.compare( u ) == 0;
              if ( success ) {
                  emit loginAttemptStatus(QString("Success..."));
              } else {
                  emit loginAttemptStatus(QString("Failure..."));
              }
              return success;
      }, username, password);
      this-&gt;watchLoginAttempt.setFuture(future);
  }
  </code></pre>
  
  <p>So, does capturing a reference to <code>this</code> going to cause problems? </p>
  
  <p>Because I think it is but I cannot find a definitive answer.</p>