title: Timer in background is very slow
body: <p>I'm working with timer and I've try to make it works in background. On simulator this works fine but on my device (iOS 11) it's very slow: 1 seconde became 5 or 6 secondes...</p>
  
  <blockquote>
    <p>This is my code for run application in background: </p>
  </blockquote>
  
  <pre><code>backgroundTaskIdentifier = UIApplication.shared.beginBackgroundTask(
      expirationHandler:
        {UIApplication.shared.endBackgroundTask(self.backgroundTaskIdentifier!)}
      )
  </code></pre>
  
  <blockquote>
    <p><strong>Info.plist:</strong>
    Application does not run in background : NO</p>
  </blockquote>
  
  <p>How can I make it works?</p>
  
  <p><strong>EDIT:</strong> </p>
  
  <p>This is my timer code: </p>
  
  <pre><code>timer = Timer.scheduledTimer(timeInterval: 0.01, target: self, 
    selector:#selector(ViewController.updateTimer), userInfo: nil, repeats: true)
  </code></pre>
  
  <p><strong>EDIT 2:</strong> </p>
  
  <pre><code>func updateTimer () {
      var j = 0
      for _ in rows {
          if (rows[j]["Playing"] as! Bool == true ) {
              rows[j]["time"] = (rows[j]["time"] as! Double + 0.01) as AnyObject
          // print(rows[j]["time"]) - PRINT OUTPUT HERE
              rows[j]["lastTime"] = (rows[j]["lastTime"] as! Double + 0.01) as AnyObject
          }
          if (rows[j]["lastTime"] as! Double &gt; 60.0) {
              min[j] += 1
              rows[j]["lastTime"] = 0.00 as AnyObject
          }
          j += 1
      }
  }
  </code></pre>