title: ARC, semaphore, convert coordinates, synchronize
body: <p>I am new to programming applications for iOS, migrating to C#. Now I write the game Tower Defence. I've got a few questions and I would be very grateful if you would help me to understand.</p>
  
  <ol>
  <li>I used to delete objects classes yourself. On iOS, I was pushed to the fact that there are ARC, which prevents me from doing it. I know that you can disable it and continue to do things the old way, but listen to the recommendations of the developers to use ARC.
  In my program checks to two intersection View ( projectile collision with Unit ) . In this case I need to remove the unit , but it is not convenient to remove all references to it from all classes in which it is used . List of units contained in NSMutableArray. How to make removing the unit from the list only , all other references to it also annulled and ARC could safely remove it?</li>
  <li>Somewhere on this forum I read that if multiple objects are working with a single list (one reads , writes another , and vice versa ) , you need to use semaphores, can you give an example of their use or refer to a well-written article?</li>
  <li>I have a View game card (primary) and it hosts subView buildings and units . Class building check units in the shot and shell creates detection . Shell is created in view from subView. How do I write building coordinates on the main view?</li>
  <li>What to use to synchronize the activities of different classes ?</li>
  </ol>
  
  <p>Thanks in advance for your answers . In my opinion rather general questions , but if you need the code snippets , write, lay out.</p>
  
  <p>And I'm sorry for my English =)</p>