gistfile1.m

- (void)_failWithConnectionError:(void(^)(NSError *error, NSDictionary *responseInfo))completion
                          caller:(dispatch_queue_t)caller
{
    NSParameterAssert(completion);
    
    if (dispatch_get_current_queue() == caller)
    {
        completion([NSError errorWithDomain:ERROR_DOMAIN
                                       code:kConnectionError
                                   userInfo:nil], nil);
    }
    else
    {
        dispatch_async(caller, ^{
            completion([NSError errorWithDomain:ERROR_DOMAIN
                                           code:kConnectionError
                                       userInfo:nil], nil);
        });
    }
}