ios - AFURLSessionManager downloadTaskWithRequest completionHandler not Asynchronous

Question

While working with the AFNetworking library I am running into an issue where after downloading JSON data into a file using the AFURLSessionManager downloadTaskWithRequest's destination param code block asynchronously, I am wanting to perform the remaining operations asynchronously as well in its completionHandler block. The problem is the completionHandler block does not seem to run asynchronously.

Would there be a need to setup a new session manager and/or download task to accomplish this. Is there perhaps a better way to do this so the operations can be performed away from the main thread in the completionHandler block.

The reason for wanting to accomplish this is to avoid tying up the main thread in case there's a huge amount of data which needs to be assigned to the self.googleResults array or rather in a for loop using a custom class containing properties for specific key data which would eventually be added as elements to an array.

Here's the code so far...

- (void)viewDidLoad
{
    [super viewDidLoad];

    AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];

    NSURL *url = [NSURL URLWithString:@"https://ajax.googleapis.com/ajax/services/search/web?v=1.0&q=json"];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];

    NSURLSessionDownloadTask *downloadTask = [manager downloadTaskWithRequest:request progress:nil destination:^NSURL *(NSURL *targetPath, NSURLResponse *response)
    {
        // NOTE: This code block runs asynchronously
        NSURL *docPathURL = [[NSFileManager defaultManager] URLForDirectory:NSDocumentDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:NO error:nil];
        return [docPathURL URLByAppendingPathComponent:[response suggestedFilename]];

    } completionHandler:^(NSURLResponse *response, NSURL *filePath, NSError *error)
    {
        // NOTE: This code block does not run asynchronously
        // Would there be a need to create a new session and/or download task here to get the data from the filePath asynchronously?
        // Or is there another way to this for the following code?
        NSError *jsonSerializationErr;
        NSData *jsonData = [NSData dataWithContentsOfURL:filePath];
        NSDictionary *reponseDictionary = [NSJSONSerialization JSONObjectWithData:jsonData options:0 error:&jsonSerializationErr];

        // self.googleResults is an instance of (NSArray *)
        self.googleResults = [[reponseDictionary objectForKey:@"responseData"] objectForKey:@"results"];
        NSLog(@"%@", self.googleResults);
    }];
    [downloadTask resume];
}