title: Strange 100% CPU usage in iOS 9 with UICollectionView
body: <p>I have a tableView, in each cell there is a collectionView. Sometimes when I know there is new data in collectionViews, I call <code>reloadData()</code> on collectionView. Most of the time this routine works, but but sometimes is starts to use 100% of CPU, memory usage increasing, GUI is blocked, and at a point app will crash. If I do not let reload collectionView, then all works well, only the content invalid in the collectionView. What is going on, in iOS 8 it was not a problem to call <code>reloadData()</code> from <code>cellForRowAtIndexPath</code>.</p>
  
  <pre><code>override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -&gt; UITableViewCell {
  
      let cell = tableView.dequeueReusableCellWithIdentifier("movie") as! MovieTableViewCell
  
      //..
  
      if cell.rcvc == nil {
  
          let cvfl = UICollectionViewFlowLayout()
          cvfl.scrollDirection = .Horizontal
          cell.rcvc = RatingCollectionViewController(collectionViewLayout: cvfl)
  
          self.addChildViewController(cell.rcvc!)
          let v = cell.viewWithTag(5)!
          v.addSubview(cell.rcvc!.view)
          cell.rcvc!.didMoveToParentViewController(self)
          cell.rcvc!.view.frame = v.bounds
      }
  
      cell.rcvc!.movie = movie
  
      if enableReloadRatingCollectionViews {
  
          cell.rcvc!.collectionView!.reloadData() // &lt;--- if I comment, not crashes
      }
  
      return cell
  }
  </code></pre>
  
  <h2>UPDATE</h2>
  
  <p>I have updated my code like @dasblinkenlight suggest, I am not calling <code>reloadData</code> anymore from <code>cellforRowAtIndexPath</code>, but now call <code>reloadData</code> for all <code>collectionView</code>s form outside when certain user interaction triggers it. But it still crashes sometimes, any idea why?</p>
  
  <pre><code>itemTableViewController!.tableView.reloadData()
  for sv in collectionViews.allObjects {
  
      (sv as! UICollectionView).reloadData()
  }
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/D3iF1.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/D3iF1.png" alt="enter image description here"></a></p>