HDFS-17735. [ARR] LocalResolver#getDatanodesSubcluster adapts to async rpc.

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/resolver/order/LocalResolver.java

@@ -45,6 +45,7 @@
 import org.apache.hadoop.classification.VisibleForTesting;
 import org.apache.hadoop.thirdparty.com.google.common.net.HostAndPort;
 
+import static org.apache.hadoop.hdfs.server.federation.router.async.utils.AsyncUtil.syncReturn;
 
 /**
  * The local subcluster (where the writer is) should be tried first. The writer
@@ -143,9 +144,16 @@ private Map<String, String> getDatanodesSubcluster() {
             @Override
             public Map<String, DatanodeStorageReport[]> run() {
               try {
-                return rpcServer.getDatanodeStorageReportMap(
-                    DatanodeReportType.ALL);
-              } catch (IOException e) {
+                Map<String, DatanodeStorageReport[]> result;
+                if (rpcServer.isAsync()) {
+                  rpcServer.getDatanodeStorageReportMapAsync(DatanodeReportType.ALL);
+                  result = syncReturn(Map.class);
+                } else {
+                  result = rpcServer.getDatanodeStorageReportMap(
+                      DatanodeReportType.ALL);
+                }
+                return result;
+              } catch (Exception e) {
                 LOG.error("Cannot get the datanodes from the RPC server", e);
                 return null;
               }

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/async/utils/AsyncUtil.java

@@ -127,7 +127,7 @@ public static <R> R syncReturn(Class<R> clazz)
     try {
       return (R) completableFuture.get();
     } catch (ExecutionException e) {
-      throw (Exception)e.getCause();
+      throw (Exception) e.getCause();
     }
   }