HADOOP-17862. ABFS: Fix unchecked cast compiler warning for AbfsListStatusRemoteIterator (#3331)

closes #3331 

Contributed by Sumangala Patki

Author: sumangala-patki

hadoop-tools/hadoop-azure/src/main/java/org/apache/hadoop/fs/azurebfs/services/AbfsListResult.java

@@ -0,0 +1,57 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.fs.azurebfs.services;
+
+import java.io.IOException;
+import java.util.Collections;
+import java.util.Iterator;
+
+import org.apache.hadoop.fs.FileStatus;
+
+/**
+ * Class to store listStatus results for AbfsListStatusRemoteIterator. The
+ * results can either be of type Iterator or an exception thrown during the
+ * operation
+ */
+public class AbfsListResult {
+  private IOException listException = null;
+
+  private Iterator<FileStatus> fileStatusIterator
+      = Collections.emptyIterator();
+
+  AbfsListResult(IOException ex) {
+    this.listException = ex;
+  }
+
+  AbfsListResult(Iterator<FileStatus> fileStatusIterator) {
+    this.fileStatusIterator = fileStatusIterator;
+  }
+
+  IOException getListingException() {
+    return listException;
+  }
+
+  Iterator<FileStatus> getFileStatusIterator() {
+    return fileStatusIterator;
+  }
+
+  boolean isFailedListing() {
+    return (listException != null);
+  }
+}

hadoop-tools/hadoop-azure/src/main/java/org/apache/hadoop/fs/azurebfs/services/AbfsListStatusRemoteIterator.java

@@ -27,7 +27,6 @@
 import java.util.concurrent.ArrayBlockingQueue;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.TimeUnit;
-import javax.activation.UnsupportedDataTypeException;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -48,7 +47,7 @@ public class AbfsListStatusRemoteIterator
 
   private final FileStatus fileStatus;
   private final ListingSupport listingSupport;
-  private final ArrayBlockingQueue<Object> iteratorsQueue;
+  private final ArrayBlockingQueue<AbfsListResult> listResultQueue;
   private final TracingContext tracingContext;
 
   private volatile boolean isAsyncInProgress = false;
@@ -61,7 +60,7 @@ public AbfsListStatusRemoteIterator(final FileStatus fileStatus,
     this.fileStatus = fileStatus;
     this.listingSupport = listingSupport;
     this.tracingContext = tracingContext;
-    iteratorsQueue = new ArrayBlockingQueue<>(MAX_QUEUE_SIZE);
+    listResultQueue = new ArrayBlockingQueue<>(MAX_QUEUE_SIZE);
     currIterator = Collections.emptyIterator();
     fetchBatchesAsync();
   }
@@ -86,19 +85,17 @@ public FileStatus next() throws IOException {
   private Iterator<FileStatus> getNextIterator() throws IOException {
     fetchBatchesAsync();
     try {
-      Object obj = null;
-      while (obj == null
-          && (!isIterationComplete || !iteratorsQueue.isEmpty())) {
-        obj = iteratorsQueue.poll(POLL_WAIT_TIME_IN_MS, TimeUnit.MILLISECONDS);
+      AbfsListResult listResult = null;
+      while (listResult == null
+          && (!isIterationComplete || !listResultQueue.isEmpty())) {
+        listResult = listResultQueue.poll(POLL_WAIT_TIME_IN_MS, TimeUnit.MILLISECONDS);
       }
-      if (obj == null) {
+      if (listResult == null) {
         return Collections.emptyIterator();
-      } else if (obj instanceof Iterator) {
-        return (Iterator<FileStatus>) obj;
-      } else if (obj instanceof IOException) {
-        throw (IOException) obj;
+      } else if (listResult.isFailedListing()) {
+        throw listResult.getListingException();
       } else {
-        throw new UnsupportedDataTypeException();
+        return listResult.getFileStatusIterator();
       }
     } catch (InterruptedException e) {
       Thread.currentThread().interrupt();
@@ -122,13 +119,13 @@ private void fetchBatchesAsync() {
 
   private void asyncOp() {
     try {
-      while (!isIterationComplete && iteratorsQueue.size() <= MAX_QUEUE_SIZE) {
+      while (!isIterationComplete && listResultQueue.size() <= MAX_QUEUE_SIZE) {
         addNextBatchIteratorToQueue();
       }
     } catch (IOException ioe) {
       LOG.error("Fetching filestatuses failed", ioe);
       try {
-        iteratorsQueue.put(ioe);
+        listResultQueue.put(new AbfsListResult(ioe));
       } catch (InterruptedException interruptedException) {
         Thread.currentThread().interrupt();
         LOG.error("Thread got interrupted: {}", interruptedException);
@@ -143,19 +140,17 @@ private void asyncOp() {
     }
   }
 
-  private void addNextBatchIteratorToQueue()
+  private synchronized void addNextBatchIteratorToQueue()
       throws IOException, InterruptedException {
     List<FileStatus> fileStatuses = new ArrayList<>();
     continuation = listingSupport
         .listStatus(fileStatus.getPath(), null, fileStatuses, FETCH_ALL_FALSE,
             continuation, tracingContext);
     if (!fileStatuses.isEmpty()) {
-      iteratorsQueue.put(fileStatuses.iterator());
+      listResultQueue.put(new AbfsListResult(fileStatuses.iterator()));
     }
-    synchronized (this) {
-      if (continuation == null || continuation.isEmpty()) {
-        isIterationComplete = true;
-      }
+    if (continuation == null || continuation.isEmpty()) {
+      isIterationComplete = true;
     }
   }