title: alternative to QOS_CLASS_UTILITY on ios7 using swift
body: <p>I'm using QOS_CLASS_UTILITY in dispatch_async to perform some async operations.Sample code is below :</p>
  
  <pre><code>dispatch_async(dispatch_get_global_queue(Int(QOS_CLASS_UTILITY.value), 0)) {
                  var ip = "163.289.2." + "\(i)"
                  let foundThisOne = Ping.getIPAddress(ip)
  
                  dispatch_async(serialQueue) {
                      if !resultFound {
                          resultFound = foundThisOne
                          numProcessed++
                          if resultFound {
                              completion(existingIP:ip)
                          } else if numProcessed == 256 {
                              completion(existingIP: nil)
                          }
                      }
                  }
              }
          }
  </code></pre>
  
  <p>But "QOS_CLASS_UTILITY" is available on iOS8 onwards and now i need to support the same logic on iOS7 also.So what is better alternative to 
  QOS_CLASS_UTILITY which works on iOS7 using swift.</p>