@Override
    public void close() throws IOException {
        closed.set(true);
        executorService.shutdownNow();
        if (httpclient instanceof Closeable) {
            ((Closeable) httpclient).close();
        }
    }
@return metrics gathered for this instance.
@see FutureRequestExecutionMetrics
httpclient5/src/main/java/org/apache/hc/client5/http/impl/classic/FutureRequestExecutionService.java