use blocking threads in hdfs object store

native-engine/datafusion-ext/src/hdfs_object_store.rs

diff --git a/native-engine/datafusion-ext/src/hdfs_object_store.rs b/native-engine/datafusion-ext/src/hdfs_object_store.rs
index 0601dba..3e5c89f 100644
--- a/native-engine/datafusion-ext/src/hdfs_object_store.rs
+++ b/native-engine/datafusion-ext/src/hdfs_object_store.rs
@@ -28,8 +28,6 @@
 use crate::jni_new_direct_byte_buffer;
 use crate::jni_new_string;
 
-const NUM_HDFS_WORKER_THREADS: usize = 64;
-
 pub struct HDFSSingleFileObjectStore {
     spawner: OnceCell<tokio::runtime::Runtime>,
 }
@@ -43,8 +41,7 @@
 
     fn spawner(&self) -> &tokio::runtime::Runtime {
         self.spawner.get_or_init(|| {
-            tokio::runtime::Builder::new_multi_thread()
-                .worker_threads(NUM_HDFS_WORKER_THREADS)
+            tokio::runtime::Builder::new_current_thread()
                 .build()
                 .unwrap()
         })