throws InterruptedException, ExecutionException {
List<DHTFuture<BootstrapEntity>> futures
= new ArrayList<DHTFuture<BootstrapEntity>>();
BootstrapConfig config = new BootstrapConfig();
config.setExecutorKey(ExecutorKey.BACKEND);
for (int i = 0; i < length; i++) {
DHTFuture<BootstrapEntity> future
= dhts.get(offset+i).bootstrap(from, config);
futures.add(future);