title: What is the parameter that @synchronized() takes
body: <p>I know what @synchronized() does, but... <br>
  sometimes we have:<br></p>
  
  <p>1- <code>@synchronized(self)</code> <br>
  2- <code>@synchronized([MyClass class])</code> <br>
  3- <code>@synchrinized(myObj)</code> <br></p>
  
  <p>What is the <b>difference</B>, and what is the parameter I should pass to this block ? </p>