 
         // Pause for 2 additional seconds to ensure all timestamps will be different
         dispatch_group_enter(dispatchGroup)
-        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, Int64(2.0 * Float(NSEC_PER_SEC))), highPriorityDispatchQueue) {
+        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, Int64(2.0 * Float(NSEC_PER_SEC))), serialQueue) {
             dispatch_group_leave(dispatchGroup)
         }
 

        -> NSURLRequest
    {
        let urlRequest = URLRequest(cacheControl: cacheControl, cachePolicy: cachePolicy)

        let request = manager.request(urlRequest)
        request.response(
            queue: queue,
            completionHandler: { _, response, data, _ in

    */
    func primeCachedResponses() {
        let dispatchGroup = dispatch_group_create()
        let serialQueue = dispatch_queue_create("com.alamofire.cache-tests", DISPATCH_QUEUE_SERIAL)

        for cacheControl in CacheControl.allValues {
            dispatch_group_enter(dispatchGroup)

            let request = startRequest(
                cacheControl: cacheControl,
                queue: serialQueue,
                completion: { _, response in
                    let timestamp = response!.allHeaderFields["Date"] as! String
                    self.timestamps[cacheControl] = timestamp
