title: NSMutableDictionary thread safety
body: <p>I have a question on thread safety while using <code>NSMutableDictionary</code>.</p>
  
  <p>The main thread is reading data from <code>NSMutableDictionary</code> where:</p>
  
  <ul>
  <li>key is <code>NSString</code></li>
  <li>value is <code>UIImage</code></li>
  </ul>
  
  <p>An asynchronous thread is writing data to above dictionary (using <code>NSOperationQueue</code>)</p>
  
  <p>How do I make the above dictionary thread safe?</p>
  
  <p>Should I make the <code>NSMutableDictionary</code> property <code>atomic</code>? Or do I need to make any additional changes?</p>
  
  <p><code>@property(retain) NSMutableDictionary *dicNamesWithPhotos;</code></p>