Core: Fix background thread leak in ScanTaskIterable

core/src/main/java/org/apache/iceberg/rest/ScanTaskIterable.java

@@ -107,7 +107,18 @@ public CloseableIterator<FileScanTask> iterator() {
   }
 
   @Override
-  public void close() throws IOException {}
+  public void close() throws IOException {
+    if (shutdown.compareAndSet(false, true)) {
+      LOG.info(
+          "ScanTaskIterable is closing. Clearing {} queued tasks, {} plan tasks, and {} initial file scan tasks.",
+          taskQueue.size(),
+          planTasks.size(),
+          initialFileScanTasks.size());
+      taskQueue.clear();
+      planTasks.clear();
+      initialFileScanTasks.clear();
+    }
+  }
 
   private class PlanTaskWorker implements Runnable {
 
@@ -278,13 +289,11 @@ public FileScanTask next() {
 
     @Override
     public void close() {
-      shutdown.set(true);
-      LOG.info(
-          "ScanTasksIterator is closing. Clearing {} queued tasks and {} plan tasks.",
-          taskQueue.size(),
-          planTasks.size());
-      taskQueue.clear();
-      planTasks.clear();
+      try {
+        ScanTaskIterable.this.close();
+      } catch (IOException e) {
+        LOG.error("Failed to cleanly close ScanTaskIterable source", e);
+      }
     }
   }
 }

core/src/test/java/org/apache/iceberg/rest/TestScanTaskIterableLeak.java

@@ -0,0 +1,80 @@
+/*
+ * 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
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 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.iceberg.rest;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+import org.apache.iceberg.FileScanTask;
+import org.apache.iceberg.io.CloseableIterable;
+import org.apache.iceberg.io.CloseableIterator;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
+
+public class TestScanTaskIterableLeak {
+
+  @Test
+  public void testBackgroundWorkerLeakOnEarlyClose() throws Exception {
+    /* * Generate tasks exceeding the default queue capacity (1000) to ensure
+     * that background PlanTaskWorker threads fill the buffer and block.
+     */
+    int totalTasks = 1050;
+    List<FileScanTask> mockTasks =
+        IntStream.range(0, totalTasks)
+            .mapToObj(i -> Mockito.mock(FileScanTask.class))
+            .collect(Collectors.toList());
+
+    ThreadPoolExecutor planningExecutor = (ThreadPoolExecutor) Executors.newFixedThreadPool(4);
+
+    ScanTaskIterable scanTaskIterable =
+        new ScanTaskIterable(
+            Collections.emptyList(),
+            mockTasks,
+            Mockito.mock(RESTClient.class),
+            null,
+            null,
+            Collections.emptyMap(),
+            planningExecutor,
+            null);
+
+    CloseableIterable<FileScanTask> wrappedIterable =
+        CloseableIterable.whenComplete(scanTaskIterable, () -> {});
+
+    CloseableIterator<FileScanTask> iterator = wrappedIterable.iterator();
+    if (iterator.hasNext()) {
+      iterator.next();
+    }
+
+    wrappedIterable.close();
+
+    Thread.sleep(2000);
+
+    int activeCount = planningExecutor.getActiveCount();
+    planningExecutor.shutdownNow();
+
+    assertThat(activeCount)
+        .as("PlanTaskWorker background threads should have terminated when the iterable closed")
+        .isEqualTo(0);
+  }
+}