title: How to do two concurrent API calls in swift 4
body: <p>Thanks in advance for help,
  I have two API calls, both are concurrent and any call could be success first(I don't want call in sequence), after success of both calls, I have to stop my activity indicator and reload my tableView,
  Here is my code but I don't know is this the right way or not and how to reload my tableView and stop my activity indicator.</p>
  
  <pre><code>func downloadDetails(){
      let operationQueue: OperationQueue = OperationQueue()
      let operation1 = BlockOperation() {
      WebServiceManager.getAData(format:A, withCompletion: {(data: Any? , error: Error?) -&gt; Void in
  
            if let success = data {
                DispatchQueue.main.async {
                    (success code)
                }
             }
          })
  
          let operation2 = BlockOperation() {
          webServiceManager.getBData(format: B, withCompletion: {(data: Any? , error: Error?) -&gt; Void in
  
                  if let success = data {
                      DispatchQueue.main.async {
                         (success code)
                      }
                  }
              })
          }
          operationQueue.addOperation(operation2)
      }
      operationQueue.addOperation(operation1)
  }
  downloadDetails() "calling function"
  </code></pre>