internal HttpRequestTaskCallable(HttpClient httpClient, IHttpUriRequest request,
HttpContext context, ResponseHandler <V> responseHandler, FutureCallback <V> callback
, FutureRequestExecutionMetrics metrics)
{
this.httpclient = httpClient;
this.responseHandler = responseHandler;
this.request = request;
this.context = context;
this.callback = callback;
this.metrics = metrics;
}