Re: [PR] [Dataflow Streaming] [Multi Key] Introduce KeyGroupWorkQueue and integrate with BoundedQueueExecutor [beam]

[via GitHub]

scwhittle commented on code in PR #38767:
URL: https://github.com/apache/beam/pull/38767#discussion_r3362639937


##########
runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/util/BoundedQueueExecutor.java:
##########
@@ -378,6 +386,22 @@ BoundedQueueExecutorWorkHandleImpl createBudgetHandle(int 
elements, long bytes)
     return new BoundedQueueExecutorWorkHandleImpl(elements, bytes);
   }
 
+  public @Nullable ExecutableWork pollWork(
+      String computationId, Work.KeyGroup keyGroup, 
BoundedQueueExecutorWorkHandle handle) {
+    checkArgument(handle instanceof BoundedQueueExecutorWorkHandleImpl);
+    checkArgument(computationId != null && keyGroup != null && 
!keyGroup.equals(KeyGroup.DEFAULT));
+    BoundedQueueExecutorWorkHandleImpl internalHandle = 
(BoundedQueueExecutorWorkHandleImpl) handle;
+    if (keyGroupWorkQueue == null) {
+      return null;
+    }
+    QueuedWork queuedWork = keyGroupWorkQueue.pollWork(computationId, 
keyGroup);

Review Comment:
   nullable



##########
runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/util/BoundedQueueExecutor.java:
##########


Review Comment:
   remove? might be able to remove some null checks below then too



##########
runners/google-cloud-dataflow-java/worker/src/test/java/org/apache/beam/runners/dataflow/worker/util/KeyGroupWorkQueueTest.java:
##########
@@ -0,0 +1,473 @@
+/*
+ * 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.beam.runners.dataflow.worker.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+import static org.mockito.Mockito.mock;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
+import org.apache.beam.runners.dataflow.worker.streaming.ExecutableWork;
+import org.apache.beam.runners.dataflow.worker.streaming.Watermarks;
+import org.apache.beam.runners.dataflow.worker.streaming.Work;
+import 
org.apache.beam.runners.dataflow.worker.util.BoundedQueueExecutor.QueuedWork;
+import org.apache.beam.runners.dataflow.worker.windmill.Windmill.WorkItem;
+import 
org.apache.beam.runners.dataflow.worker.windmill.client.getdata.FakeGetDataClient;
+import 
org.apache.beam.runners.dataflow.worker.windmill.work.refresh.HeartbeatSender;
+import org.apache.beam.vendor.grpc.v1p69p0.com.google.protobuf.ByteString;
+import 
org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.util.concurrent.ThreadFactoryBuilder;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.joda.time.Instant;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameters;
+
+@RunWith(Parameterized.class)
+public class KeyGroupWorkQueueTest {
+
+  @Parameters(name = "fairQueue={0}")
+  public static Iterable<Object[]> data() {
+    return Arrays.asList(new Object[][] {{true}, {false}});
+  }
+
+  @Parameterized.Parameter public boolean fairQueue;
+
+  private BoundedQueueExecutor executor;
+
+  @Before
+  public void setUp() {
+    executor =
+        new BoundedQueueExecutor(
+            2,
+            60,
+            TimeUnit.SECONDS,
+            100,
+            10000000,
+            new 
ThreadFactoryBuilder().setNameFormat("Test-%d").setDaemon(true).build(),
+            fairQueue,
+            /*useKeyGroupWorkQueue=*/ true);
+  }
+
+  private static final Work.KeyGroup TEST_KEY_GROUP = Work.KeyGroup.create(1, 
2);
+
+  private QueuedWork createQueuedWork(String computationId, long workBytes) {
+    return createQueuedWork(computationId, TEST_KEY_GROUP, workBytes);
+  }
+
+  private QueuedWork createQueuedWork(
+      String computationId, Work.@Nullable KeyGroup keyGroup, long workBytes) {
+    WorkItem.Builder workItemBuilder =
+        WorkItem.newBuilder()
+            .setKey(ByteString.EMPTY)
+            .setShardingKey(1)
+            .setWorkToken(33)
+            .setCacheToken(1);
+    if (keyGroup != null) {
+      workItemBuilder.setKeyGroup(
+          
org.apache.beam.runners.dataflow.worker.windmill.Windmill.Uint128Proto.newBuilder()
+              .setHigh(keyGroup.high())
+              .setLow(keyGroup.low())
+              .build());
+    }
+    WorkItem workItem = workItemBuilder.build();
+    ExecutableWork work =
+        ExecutableWork.create(
+            Work.create(
+                workItem,
+                workItem.getSerializedSize(),
+                
Watermarks.builder().setInputDataWatermark(Instant.now()).build(),
+                Work.createProcessingContext(
+                    computationId,
+                    new FakeGetDataClient(),
+                    ignored -> {},
+                    mock(HeartbeatSender.class)),
+                false,
+                Instant::now),
+            (w, h) -> {});
+    return new QueuedWork(work, executor.createBudgetHandle(1, workBytes));
+  }
+
+  private static class MockRunnable implements Runnable {
+    final String id;
+
+    MockRunnable(String id) {
+      this.id = id;
+    }
+
+    @Override
+    public void run() {}
+
+    @Override
+    public String toString() {
+      return "MockRunnable(" + id + ")";
+    }
+  }
+
+  @Test
+  public void testBasicOfferAndPoll() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    assertTrue(queue.isEmpty());
+    assertEquals(0, queue.size());
+
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+
+    assertTrue(queue.offer(task1));
+    assertTrue(queue.offer(task2));
+    assertEquals(2, queue.size());
+
+    assertEquals(task1, queue.poll());
+    assertEquals(task2, queue.poll());
+    assertNull(queue.poll());
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testRemove() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+
+    queue.offer(task1);
+    queue.offer(task2);
+
+    assertTrue(queue.remove(task1));
+    assertEquals(1, queue.size());
+    assertEquals(task2, queue.poll());
+    assertFalse(queue.remove(task1)); // Already gone
+  }
+
+  @Test
+  public void testDrainTo() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+    queue.offer(task1);
+    queue.offer(task2);
+
+    List<Runnable> drained = new ArrayList<>();
+    assertEquals(2, queue.drainTo(drained));
+    assertEquals(2, drained.size());
+    assertEquals(task1, drained.get(0));
+    assertEquals(task2, drained.get(1));
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testIteratorSafeTraversalAndImmutable() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+    queue.offer(task1);
+    queue.offer(task2);
+
+    Iterator<Runnable> it = queue.iterator();
+    assertTrue(it.hasNext());
+    assertEquals(task1, it.next());
+    assertTrue(it.hasNext());
+    assertEquals(task2, it.next());
+    assertFalse(it.hasNext());
+
+    // Assert that mutating the iterator throws UnsupportedOperationException
+    it = queue.iterator();
+    assertTrue(it.hasNext());
+    it.next();
+    try {
+      it.remove();
+      fail("Iterator must be immutable");
+    } catch (UnsupportedOperationException e) {
+      // Expected
+    }
+  }
+
+  @Test
+  public void testPollWorkTargeted() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+
+    QueuedWork workA1 = createQueuedWork("compA", 100);
+    QueuedWork workB1 = createQueuedWork("compB", 200);
+    QueuedWork workA2 = createQueuedWork("compA", 150);
+
+    queue.offer(workA1);
+    queue.offer(workB1);
+    queue.offer(workA2);
+
+    assertEquals(3, queue.size());
+
+    // Targeted poll A
+    QueuedWork polledA1 = queue.pollWork("compA", TEST_KEY_GROUP);
+    assertNotNull(polledA1);
+    assertEquals("compA", polledA1.getWork().getComputationId());
+    assertEquals(100, polledA1.getHandle().bytes());
+
+    // Verify size decremented
+    assertEquals(2, queue.size());
+
+    // Poll next should be B1 (since A1 was stolen, B1 is now first global)
+    assertEquals(workB1, queue.poll());
+    assertEquals(1, queue.size());
+
+    // Last should be A2
+    assertEquals(workA2, queue.poll());
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testMemoryPruningLeavesZeroLeaks() {

Review Comment:
   not sure what memorypruning means here or how leaks is being validated.  Can 
you just add size checking to other tests and remove this one?



##########
runners/google-cloud-dataflow-java/worker/src/test/java/org/apache/beam/runners/dataflow/worker/util/KeyGroupWorkQueueTest.java:
##########
@@ -0,0 +1,473 @@
+/*
+ * 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.beam.runners.dataflow.worker.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+import static org.mockito.Mockito.mock;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
+import org.apache.beam.runners.dataflow.worker.streaming.ExecutableWork;
+import org.apache.beam.runners.dataflow.worker.streaming.Watermarks;
+import org.apache.beam.runners.dataflow.worker.streaming.Work;
+import 
org.apache.beam.runners.dataflow.worker.util.BoundedQueueExecutor.QueuedWork;
+import org.apache.beam.runners.dataflow.worker.windmill.Windmill.WorkItem;
+import 
org.apache.beam.runners.dataflow.worker.windmill.client.getdata.FakeGetDataClient;
+import 
org.apache.beam.runners.dataflow.worker.windmill.work.refresh.HeartbeatSender;
+import org.apache.beam.vendor.grpc.v1p69p0.com.google.protobuf.ByteString;
+import 
org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.util.concurrent.ThreadFactoryBuilder;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.joda.time.Instant;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameters;
+
+@RunWith(Parameterized.class)
+public class KeyGroupWorkQueueTest {
+
+  @Parameters(name = "fairQueue={0}")
+  public static Iterable<Object[]> data() {
+    return Arrays.asList(new Object[][] {{true}, {false}});
+  }
+
+  @Parameterized.Parameter public boolean fairQueue;
+
+  private BoundedQueueExecutor executor;
+
+  @Before
+  public void setUp() {
+    executor =
+        new BoundedQueueExecutor(
+            2,
+            60,
+            TimeUnit.SECONDS,
+            100,
+            10000000,
+            new 
ThreadFactoryBuilder().setNameFormat("Test-%d").setDaemon(true).build(),
+            fairQueue,
+            /*useKeyGroupWorkQueue=*/ true);
+  }
+
+  private static final Work.KeyGroup TEST_KEY_GROUP = Work.KeyGroup.create(1, 
2);
+
+  private QueuedWork createQueuedWork(String computationId, long workBytes) {
+    return createQueuedWork(computationId, TEST_KEY_GROUP, workBytes);
+  }
+
+  private QueuedWork createQueuedWork(
+      String computationId, Work.@Nullable KeyGroup keyGroup, long workBytes) {
+    WorkItem.Builder workItemBuilder =
+        WorkItem.newBuilder()
+            .setKey(ByteString.EMPTY)
+            .setShardingKey(1)
+            .setWorkToken(33)
+            .setCacheToken(1);
+    if (keyGroup != null) {
+      workItemBuilder.setKeyGroup(
+          
org.apache.beam.runners.dataflow.worker.windmill.Windmill.Uint128Proto.newBuilder()
+              .setHigh(keyGroup.high())
+              .setLow(keyGroup.low())
+              .build());
+    }
+    WorkItem workItem = workItemBuilder.build();
+    ExecutableWork work =
+        ExecutableWork.create(
+            Work.create(
+                workItem,
+                workItem.getSerializedSize(),
+                
Watermarks.builder().setInputDataWatermark(Instant.now()).build(),
+                Work.createProcessingContext(
+                    computationId,
+                    new FakeGetDataClient(),
+                    ignored -> {},
+                    mock(HeartbeatSender.class)),
+                false,
+                Instant::now),
+            (w, h) -> {});
+    return new QueuedWork(work, executor.createBudgetHandle(1, workBytes));
+  }
+
+  private static class MockRunnable implements Runnable {
+    final String id;
+
+    MockRunnable(String id) {
+      this.id = id;
+    }
+
+    @Override
+    public void run() {}
+
+    @Override
+    public String toString() {
+      return "MockRunnable(" + id + ")";
+    }
+  }
+
+  @Test
+  public void testBasicOfferAndPoll() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    assertTrue(queue.isEmpty());
+    assertEquals(0, queue.size());
+
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+
+    assertTrue(queue.offer(task1));
+    assertTrue(queue.offer(task2));
+    assertEquals(2, queue.size());
+
+    assertEquals(task1, queue.poll());
+    assertEquals(task2, queue.poll());
+    assertNull(queue.poll());
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testRemove() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+
+    queue.offer(task1);
+    queue.offer(task2);
+
+    assertTrue(queue.remove(task1));
+    assertEquals(1, queue.size());
+    assertEquals(task2, queue.poll());
+    assertFalse(queue.remove(task1)); // Already gone
+  }
+
+  @Test
+  public void testDrainTo() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+    queue.offer(task1);
+    queue.offer(task2);
+
+    List<Runnable> drained = new ArrayList<>();
+    assertEquals(2, queue.drainTo(drained));
+    assertEquals(2, drained.size());
+    assertEquals(task1, drained.get(0));
+    assertEquals(task2, drained.get(1));
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testIteratorSafeTraversalAndImmutable() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+    queue.offer(task1);
+    queue.offer(task2);
+
+    Iterator<Runnable> it = queue.iterator();
+    assertTrue(it.hasNext());
+    assertEquals(task1, it.next());
+    assertTrue(it.hasNext());
+    assertEquals(task2, it.next());
+    assertFalse(it.hasNext());
+
+    // Assert that mutating the iterator throws UnsupportedOperationException
+    it = queue.iterator();
+    assertTrue(it.hasNext());
+    it.next();
+    try {
+      it.remove();
+      fail("Iterator must be immutable");
+    } catch (UnsupportedOperationException e) {
+      // Expected
+    }
+  }
+
+  @Test
+  public void testPollWorkTargeted() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+
+    QueuedWork workA1 = createQueuedWork("compA", 100);
+    QueuedWork workB1 = createQueuedWork("compB", 200);
+    QueuedWork workA2 = createQueuedWork("compA", 150);
+
+    queue.offer(workA1);
+    queue.offer(workB1);
+    queue.offer(workA2);
+
+    assertEquals(3, queue.size());
+
+    // Targeted poll A
+    QueuedWork polledA1 = queue.pollWork("compA", TEST_KEY_GROUP);
+    assertNotNull(polledA1);
+    assertEquals("compA", polledA1.getWork().getComputationId());
+    assertEquals(100, polledA1.getHandle().bytes());
+
+    // Verify size decremented
+    assertEquals(2, queue.size());
+
+    // Poll next should be B1 (since A1 was stolen, B1 is now first global)
+    assertEquals(workB1, queue.poll());
+    assertEquals(1, queue.size());
+
+    // Last should be A2
+    assertEquals(workA2, queue.poll());
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testMemoryPruningLeavesZeroLeaks() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    QueuedWork workA1 = createQueuedWork("compA", 100);
+    queue.offer(workA1);
+
+    // Steal A1
+    QueuedWork polled = queue.pollWork("compA", TEST_KEY_GROUP);
+    assertNotNull(polled);
+    assertTrue(queue.isEmpty());
+
+    // Offering another work with different computation ID
+    QueuedWork workB1 = createQueuedWork("compB", 200);
+    queue.offer(workB1);
+    assertEquals(1, queue.size());
+
+    // Steal B1
+    QueuedWork polledB = queue.pollWork("compB", TEST_KEY_GROUP);
+    assertNotNull(polledB);
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testConcurrentStress() throws InterruptedException, 
ExecutionException {
+    final KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    final int producerThreads = 4;
+    final int consumerThreads = 4;
+    final int tasksPerProducer = 1000;
+    final int totalTasks = producerThreads * tasksPerProducer;
+
+    ExecutorService executorService =
+        Executors.newFixedThreadPool(producerThreads + consumerThreads);
+    final CountDownLatch startLatch = new CountDownLatch(1);
+    final CountDownLatch doneLatch = new CountDownLatch(producerThreads + 
consumerThreads);
+    final AtomicInteger consumedCount = new AtomicInteger(0);
+    List<Future<?>> futures = new ArrayList<>();
+
+    // Start producers
+    for (int i = 0; i < producerThreads; i++) {
+      futures.add(
+          executorService.submit(
+              () -> {
+                try {
+                  startLatch.await();
+                  for (int j = 0; j < tasksPerProducer; j++) {
+                    String compId = "comp-" + (j % 5);
+                    queue.offer(createQueuedWork(compId, 10));
+                  }
+                } catch (Exception e) {
+                  throw new RuntimeException(e);
+                } finally {
+                  doneLatch.countDown();
+                }
+              }));
+    }
+
+    // Start consumers (mix of poll and pollWork)
+    for (int i = 0; i < consumerThreads; i++) {
+      final int consumerId = i;
+      futures.add(
+          executorService.submit(
+              () -> {
+                try {
+                  startLatch.await();
+                  while (consumedCount.get() < totalTasks) {
+                    Runnable task;
+                    if (consumerId % 2 == 0) {
+                      // Targeted poll
+                      String compId = "comp-" + (consumedCount.get() % 5);
+                      task = queue.pollWork(compId, TEST_KEY_GROUP);
+                    } else {
+                      // Global poll
+                      task = queue.poll();
+                    }
+                    if (task != null) {
+                      consumedCount.incrementAndGet();
+                    }
+                  }
+                } catch (Exception e) {
+                  throw new RuntimeException(e);
+                } finally {
+                  doneLatch.countDown();
+                }
+              }));
+    }
+
+    startLatch.countDown();
+    assertTrue(doneLatch.await(10, TimeUnit.SECONDS));
+
+    // Check for exceptions in threads
+    for (Future<?> future : futures) {
+      future.get();
+    }
+
+    executorService.shutdown();
+    assertTrue(executorService.awaitTermination(5, TimeUnit.SECONDS));
+
+    assertEquals(0, queue.size());
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testTakeBlocksAndWakesUp() throws InterruptedException {
+    final KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    final MockRunnable task = new MockRunnable("take-task");
+    final AtomicReference<Runnable> result = new AtomicReference<>();
+    final CountDownLatch started = new CountDownLatch(1);
+    final CountDownLatch finished = new CountDownLatch(1);
+
+    Thread t =
+        new Thread(
+            () -> {
+              started.countDown();
+              try {
+                result.set(queue.take());
+              } catch (InterruptedException e) {
+                // Ignore
+              } finally {
+                finished.countDown();
+              }
+            });
+    t.setDaemon(true);
+    t.start();
+
+    assertTrue(started.await(2, TimeUnit.SECONDS));

Review Comment:
   higher timeouts here so it isn't flaky? ditto below



##########
runners/google-cloud-dataflow-java/worker/src/test/java/org/apache/beam/runners/dataflow/worker/util/KeyGroupWorkQueueTest.java:
##########
@@ -0,0 +1,473 @@
+/*
+ * 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.beam.runners.dataflow.worker.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+import static org.mockito.Mockito.mock;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
+import org.apache.beam.runners.dataflow.worker.streaming.ExecutableWork;
+import org.apache.beam.runners.dataflow.worker.streaming.Watermarks;
+import org.apache.beam.runners.dataflow.worker.streaming.Work;
+import 
org.apache.beam.runners.dataflow.worker.util.BoundedQueueExecutor.QueuedWork;
+import org.apache.beam.runners.dataflow.worker.windmill.Windmill.WorkItem;
+import 
org.apache.beam.runners.dataflow.worker.windmill.client.getdata.FakeGetDataClient;
+import 
org.apache.beam.runners.dataflow.worker.windmill.work.refresh.HeartbeatSender;
+import org.apache.beam.vendor.grpc.v1p69p0.com.google.protobuf.ByteString;
+import 
org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.util.concurrent.ThreadFactoryBuilder;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.joda.time.Instant;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameters;
+
+@RunWith(Parameterized.class)
+public class KeyGroupWorkQueueTest {
+
+  @Parameters(name = "fairQueue={0}")
+  public static Iterable<Object[]> data() {
+    return Arrays.asList(new Object[][] {{true}, {false}});
+  }
+
+  @Parameterized.Parameter public boolean fairQueue;
+
+  private BoundedQueueExecutor executor;
+
+  @Before
+  public void setUp() {
+    executor =
+        new BoundedQueueExecutor(
+            2,
+            60,
+            TimeUnit.SECONDS,
+            100,
+            10000000,
+            new 
ThreadFactoryBuilder().setNameFormat("Test-%d").setDaemon(true).build(),
+            fairQueue,
+            /*useKeyGroupWorkQueue=*/ true);
+  }
+
+  private static final Work.KeyGroup TEST_KEY_GROUP = Work.KeyGroup.create(1, 
2);
+
+  private QueuedWork createQueuedWork(String computationId, long workBytes) {
+    return createQueuedWork(computationId, TEST_KEY_GROUP, workBytes);
+  }
+
+  private QueuedWork createQueuedWork(
+      String computationId, Work.@Nullable KeyGroup keyGroup, long workBytes) {
+    WorkItem.Builder workItemBuilder =
+        WorkItem.newBuilder()
+            .setKey(ByteString.EMPTY)
+            .setShardingKey(1)
+            .setWorkToken(33)
+            .setCacheToken(1);
+    if (keyGroup != null) {
+      workItemBuilder.setKeyGroup(
+          
org.apache.beam.runners.dataflow.worker.windmill.Windmill.Uint128Proto.newBuilder()
+              .setHigh(keyGroup.high())
+              .setLow(keyGroup.low())
+              .build());
+    }
+    WorkItem workItem = workItemBuilder.build();
+    ExecutableWork work =
+        ExecutableWork.create(
+            Work.create(
+                workItem,
+                workItem.getSerializedSize(),
+                
Watermarks.builder().setInputDataWatermark(Instant.now()).build(),
+                Work.createProcessingContext(
+                    computationId,
+                    new FakeGetDataClient(),
+                    ignored -> {},
+                    mock(HeartbeatSender.class)),
+                false,
+                Instant::now),
+            (w, h) -> {});
+    return new QueuedWork(work, executor.createBudgetHandle(1, workBytes));
+  }
+
+  private static class MockRunnable implements Runnable {
+    final String id;
+
+    MockRunnable(String id) {
+      this.id = id;
+    }
+
+    @Override
+    public void run() {}
+
+    @Override
+    public String toString() {
+      return "MockRunnable(" + id + ")";
+    }
+  }
+
+  @Test
+  public void testBasicOfferAndPoll() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    assertTrue(queue.isEmpty());
+    assertEquals(0, queue.size());
+
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+
+    assertTrue(queue.offer(task1));
+    assertTrue(queue.offer(task2));
+    assertEquals(2, queue.size());
+
+    assertEquals(task1, queue.poll());
+    assertEquals(task2, queue.poll());
+    assertNull(queue.poll());
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testRemove() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+
+    queue.offer(task1);
+    queue.offer(task2);
+
+    assertTrue(queue.remove(task1));
+    assertEquals(1, queue.size());
+    assertEquals(task2, queue.poll());
+    assertFalse(queue.remove(task1)); // Already gone
+  }
+
+  @Test
+  public void testDrainTo() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+    queue.offer(task1);
+    queue.offer(task2);
+
+    List<Runnable> drained = new ArrayList<>();
+    assertEquals(2, queue.drainTo(drained));
+    assertEquals(2, drained.size());
+    assertEquals(task1, drained.get(0));
+    assertEquals(task2, drained.get(1));
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testIteratorSafeTraversalAndImmutable() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+    queue.offer(task1);
+    queue.offer(task2);
+
+    Iterator<Runnable> it = queue.iterator();
+    assertTrue(it.hasNext());
+    assertEquals(task1, it.next());
+    assertTrue(it.hasNext());
+    assertEquals(task2, it.next());
+    assertFalse(it.hasNext());
+
+    // Assert that mutating the iterator throws UnsupportedOperationException
+    it = queue.iterator();
+    assertTrue(it.hasNext());
+    it.next();
+    try {
+      it.remove();
+      fail("Iterator must be immutable");
+    } catch (UnsupportedOperationException e) {
+      // Expected
+    }
+  }
+
+  @Test
+  public void testPollWorkTargeted() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+
+    QueuedWork workA1 = createQueuedWork("compA", 100);
+    QueuedWork workB1 = createQueuedWork("compB", 200);
+    QueuedWork workA2 = createQueuedWork("compA", 150);
+
+    queue.offer(workA1);
+    queue.offer(workB1);
+    queue.offer(workA2);
+
+    assertEquals(3, queue.size());
+
+    // Targeted poll A
+    QueuedWork polledA1 = queue.pollWork("compA", TEST_KEY_GROUP);
+    assertNotNull(polledA1);
+    assertEquals("compA", polledA1.getWork().getComputationId());
+    assertEquals(100, polledA1.getHandle().bytes());
+
+    // Verify size decremented
+    assertEquals(2, queue.size());
+
+    // Poll next should be B1 (since A1 was stolen, B1 is now first global)
+    assertEquals(workB1, queue.poll());
+    assertEquals(1, queue.size());
+
+    // Last should be A2
+    assertEquals(workA2, queue.poll());
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testMemoryPruningLeavesZeroLeaks() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    QueuedWork workA1 = createQueuedWork("compA", 100);
+    queue.offer(workA1);
+
+    // Steal A1
+    QueuedWork polled = queue.pollWork("compA", TEST_KEY_GROUP);
+    assertNotNull(polled);
+    assertTrue(queue.isEmpty());
+
+    // Offering another work with different computation ID
+    QueuedWork workB1 = createQueuedWork("compB", 200);
+    queue.offer(workB1);
+    assertEquals(1, queue.size());
+
+    // Steal B1
+    QueuedWork polledB = queue.pollWork("compB", TEST_KEY_GROUP);
+    assertNotNull(polledB);
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testConcurrentStress() throws InterruptedException, 
ExecutionException {
+    final KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    final int producerThreads = 4;
+    final int consumerThreads = 4;
+    final int tasksPerProducer = 1000;
+    final int totalTasks = producerThreads * tasksPerProducer;
+
+    ExecutorService executorService =
+        Executors.newFixedThreadPool(producerThreads + consumerThreads);
+    final CountDownLatch startLatch = new CountDownLatch(1);
+    final CountDownLatch doneLatch = new CountDownLatch(producerThreads + 
consumerThreads);
+    final AtomicInteger consumedCount = new AtomicInteger(0);
+    List<Future<?>> futures = new ArrayList<>();
+
+    // Start producers
+    for (int i = 0; i < producerThreads; i++) {
+      futures.add(
+          executorService.submit(
+              () -> {
+                try {
+                  startLatch.await();
+                  for (int j = 0; j < tasksPerProducer; j++) {
+                    String compId = "comp-" + (j % 5);
+                    queue.offer(createQueuedWork(compId, 10));
+                  }
+                } catch (Exception e) {
+                  throw new RuntimeException(e);
+                } finally {
+                  doneLatch.countDown();
+                }
+              }));
+    }
+
+    // Start consumers (mix of poll and pollWork)
+    for (int i = 0; i < consumerThreads; i++) {
+      final int consumerId = i;
+      futures.add(
+          executorService.submit(
+              () -> {
+                try {
+                  startLatch.await();
+                  while (consumedCount.get() < totalTasks) {
+                    Runnable task;
+                    if (consumerId % 2 == 0) {
+                      // Targeted poll
+                      String compId = "comp-" + (consumedCount.get() % 5);
+                      task = queue.pollWork(compId, TEST_KEY_GROUP);
+                    } else {
+                      // Global poll
+                      task = queue.poll();
+                    }
+                    if (task != null) {
+                      consumedCount.incrementAndGet();
+                    }
+                  }
+                } catch (Exception e) {
+                  throw new RuntimeException(e);
+                } finally {
+                  doneLatch.countDown();
+                }
+              }));
+    }
+
+    startLatch.countDown();
+    assertTrue(doneLatch.await(10, TimeUnit.SECONDS));
+
+    // Check for exceptions in threads
+    for (Future<?> future : futures) {
+      future.get();
+    }
+
+    executorService.shutdown();
+    assertTrue(executorService.awaitTermination(5, TimeUnit.SECONDS));
+
+    assertEquals(0, queue.size());
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testTakeBlocksAndWakesUp() throws InterruptedException {
+    final KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    final MockRunnable task = new MockRunnable("take-task");
+    final AtomicReference<Runnable> result = new AtomicReference<>();
+    final CountDownLatch started = new CountDownLatch(1);
+    final CountDownLatch finished = new CountDownLatch(1);
+
+    Thread t =
+        new Thread(
+            () -> {
+              started.countDown();
+              try {
+                result.set(queue.take());
+              } catch (InterruptedException e) {
+                // Ignore
+              } finally {
+                finished.countDown();
+              }
+            });
+    t.setDaemon(true);
+    t.start();
+
+    assertTrue(started.await(2, TimeUnit.SECONDS));
+    // Give thread a moment to enter await()
+    Thread.sleep(100);
+    assertEquals(Thread.State.WAITING, t.getState());
+
+    queue.offer(task);
+
+    assertTrue(finished.await(2, TimeUnit.SECONDS));
+    assertEquals(task, result.get());
+  }
+
+  @Test
+  public void testPollWithTimeout() throws InterruptedException {
+    final KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    final MockRunnable task = new MockRunnable("poll-task");
+    final AtomicReference<Runnable> result = new AtomicReference<>();
+    final CountDownLatch started = new CountDownLatch(1);
+    final CountDownLatch finished = new CountDownLatch(1);
+
+    // 1. Verify timeout returns null
+    Thread t1 =
+        new Thread(
+            () -> {
+              started.countDown();
+              try {
+                result.set(queue.poll(500, TimeUnit.MILLISECONDS));
+              } catch (InterruptedException e) {
+                // Ignore
+              } finally {
+                finished.countDown();
+              }
+            });
+    t1.setDaemon(true);
+    t1.start();
+
+    assertTrue(started.await(2, TimeUnit.SECONDS));
+    Thread.sleep(100);
+    assertEquals(Thread.State.TIMED_WAITING, t1.getState());
+
+    assertTrue(finished.await(2, TimeUnit.SECONDS));
+    assertNull(result.get());
+
+    // 2. Verify timed poll receives task offered concurrently
+    final CountDownLatch started2 = new CountDownLatch(1);
+    final CountDownLatch finished2 = new CountDownLatch(1);
+    final AtomicReference<Runnable> result2 = new AtomicReference<>();
+
+    Thread t2 =
+        new Thread(
+            () -> {
+              started2.countDown();
+              try {
+                result2.set(queue.poll(2, TimeUnit.SECONDS));

Review Comment:
   ditto higher so not flaky



##########
runners/google-cloud-dataflow-java/worker/src/test/java/org/apache/beam/runners/dataflow/worker/util/KeyGroupWorkQueueTest.java:
##########
@@ -0,0 +1,473 @@
+/*
+ * 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.beam.runners.dataflow.worker.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+import static org.mockito.Mockito.mock;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
+import org.apache.beam.runners.dataflow.worker.streaming.ExecutableWork;
+import org.apache.beam.runners.dataflow.worker.streaming.Watermarks;
+import org.apache.beam.runners.dataflow.worker.streaming.Work;
+import 
org.apache.beam.runners.dataflow.worker.util.BoundedQueueExecutor.QueuedWork;
+import org.apache.beam.runners.dataflow.worker.windmill.Windmill.WorkItem;
+import 
org.apache.beam.runners.dataflow.worker.windmill.client.getdata.FakeGetDataClient;
+import 
org.apache.beam.runners.dataflow.worker.windmill.work.refresh.HeartbeatSender;
+import org.apache.beam.vendor.grpc.v1p69p0.com.google.protobuf.ByteString;
+import 
org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.util.concurrent.ThreadFactoryBuilder;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.joda.time.Instant;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameters;
+
+@RunWith(Parameterized.class)
+public class KeyGroupWorkQueueTest {
+
+  @Parameters(name = "fairQueue={0}")
+  public static Iterable<Object[]> data() {
+    return Arrays.asList(new Object[][] {{true}, {false}});
+  }
+
+  @Parameterized.Parameter public boolean fairQueue;
+
+  private BoundedQueueExecutor executor;
+
+  @Before
+  public void setUp() {
+    executor =
+        new BoundedQueueExecutor(
+            2,
+            60,
+            TimeUnit.SECONDS,
+            100,
+            10000000,
+            new 
ThreadFactoryBuilder().setNameFormat("Test-%d").setDaemon(true).build(),
+            fairQueue,
+            /*useKeyGroupWorkQueue=*/ true);
+  }
+
+  private static final Work.KeyGroup TEST_KEY_GROUP = Work.KeyGroup.create(1, 
2);
+
+  private QueuedWork createQueuedWork(String computationId, long workBytes) {
+    return createQueuedWork(computationId, TEST_KEY_GROUP, workBytes);
+  }
+
+  private QueuedWork createQueuedWork(
+      String computationId, Work.@Nullable KeyGroup keyGroup, long workBytes) {
+    WorkItem.Builder workItemBuilder =
+        WorkItem.newBuilder()
+            .setKey(ByteString.EMPTY)
+            .setShardingKey(1)
+            .setWorkToken(33)
+            .setCacheToken(1);
+    if (keyGroup != null) {
+      workItemBuilder.setKeyGroup(
+          
org.apache.beam.runners.dataflow.worker.windmill.Windmill.Uint128Proto.newBuilder()
+              .setHigh(keyGroup.high())
+              .setLow(keyGroup.low())
+              .build());
+    }
+    WorkItem workItem = workItemBuilder.build();
+    ExecutableWork work =
+        ExecutableWork.create(
+            Work.create(
+                workItem,
+                workItem.getSerializedSize(),
+                
Watermarks.builder().setInputDataWatermark(Instant.now()).build(),
+                Work.createProcessingContext(
+                    computationId,
+                    new FakeGetDataClient(),
+                    ignored -> {},
+                    mock(HeartbeatSender.class)),
+                false,
+                Instant::now),
+            (w, h) -> {});
+    return new QueuedWork(work, executor.createBudgetHandle(1, workBytes));
+  }
+
+  private static class MockRunnable implements Runnable {

Review Comment:
   nit: NoOpRunnable or FakeRunnable



##########
runners/google-cloud-dataflow-java/worker/src/test/java/org/apache/beam/runners/dataflow/worker/util/KeyGroupWorkQueueTest.java:
##########
@@ -0,0 +1,473 @@
+/*
+ * 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.beam.runners.dataflow.worker.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+import static org.mockito.Mockito.mock;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
+import org.apache.beam.runners.dataflow.worker.streaming.ExecutableWork;
+import org.apache.beam.runners.dataflow.worker.streaming.Watermarks;
+import org.apache.beam.runners.dataflow.worker.streaming.Work;
+import 
org.apache.beam.runners.dataflow.worker.util.BoundedQueueExecutor.QueuedWork;
+import org.apache.beam.runners.dataflow.worker.windmill.Windmill.WorkItem;
+import 
org.apache.beam.runners.dataflow.worker.windmill.client.getdata.FakeGetDataClient;
+import 
org.apache.beam.runners.dataflow.worker.windmill.work.refresh.HeartbeatSender;
+import org.apache.beam.vendor.grpc.v1p69p0.com.google.protobuf.ByteString;
+import 
org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.util.concurrent.ThreadFactoryBuilder;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.joda.time.Instant;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameters;
+
+@RunWith(Parameterized.class)
+public class KeyGroupWorkQueueTest {
+
+  @Parameters(name = "fairQueue={0}")
+  public static Iterable<Object[]> data() {
+    return Arrays.asList(new Object[][] {{true}, {false}});
+  }
+
+  @Parameterized.Parameter public boolean fairQueue;
+
+  private BoundedQueueExecutor executor;
+
+  @Before
+  public void setUp() {
+    executor =
+        new BoundedQueueExecutor(
+            2,
+            60,
+            TimeUnit.SECONDS,
+            100,
+            10000000,
+            new 
ThreadFactoryBuilder().setNameFormat("Test-%d").setDaemon(true).build(),
+            fairQueue,
+            /*useKeyGroupWorkQueue=*/ true);
+  }
+
+  private static final Work.KeyGroup TEST_KEY_GROUP = Work.KeyGroup.create(1, 
2);
+
+  private QueuedWork createQueuedWork(String computationId, long workBytes) {
+    return createQueuedWork(computationId, TEST_KEY_GROUP, workBytes);
+  }
+
+  private QueuedWork createQueuedWork(
+      String computationId, Work.@Nullable KeyGroup keyGroup, long workBytes) {
+    WorkItem.Builder workItemBuilder =
+        WorkItem.newBuilder()
+            .setKey(ByteString.EMPTY)
+            .setShardingKey(1)
+            .setWorkToken(33)
+            .setCacheToken(1);
+    if (keyGroup != null) {
+      workItemBuilder.setKeyGroup(
+          
org.apache.beam.runners.dataflow.worker.windmill.Windmill.Uint128Proto.newBuilder()
+              .setHigh(keyGroup.high())
+              .setLow(keyGroup.low())
+              .build());
+    }
+    WorkItem workItem = workItemBuilder.build();
+    ExecutableWork work =
+        ExecutableWork.create(
+            Work.create(
+                workItem,
+                workItem.getSerializedSize(),
+                
Watermarks.builder().setInputDataWatermark(Instant.now()).build(),
+                Work.createProcessingContext(
+                    computationId,
+                    new FakeGetDataClient(),
+                    ignored -> {},
+                    mock(HeartbeatSender.class)),
+                false,
+                Instant::now),
+            (w, h) -> {});
+    return new QueuedWork(work, executor.createBudgetHandle(1, workBytes));
+  }
+
+  private static class MockRunnable implements Runnable {
+    final String id;
+
+    MockRunnable(String id) {
+      this.id = id;
+    }
+
+    @Override
+    public void run() {}
+
+    @Override
+    public String toString() {
+      return "MockRunnable(" + id + ")";
+    }
+  }
+
+  @Test
+  public void testBasicOfferAndPoll() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    assertTrue(queue.isEmpty());
+    assertEquals(0, queue.size());
+
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+
+    assertTrue(queue.offer(task1));
+    assertTrue(queue.offer(task2));
+    assertEquals(2, queue.size());
+
+    assertEquals(task1, queue.poll());
+    assertEquals(task2, queue.poll());
+    assertNull(queue.poll());
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testRemove() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+
+    queue.offer(task1);
+    queue.offer(task2);
+
+    assertTrue(queue.remove(task1));
+    assertEquals(1, queue.size());
+    assertEquals(task2, queue.poll());
+    assertFalse(queue.remove(task1)); // Already gone
+  }
+
+  @Test
+  public void testDrainTo() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+    queue.offer(task1);
+    queue.offer(task2);
+
+    List<Runnable> drained = new ArrayList<>();
+    assertEquals(2, queue.drainTo(drained));
+    assertEquals(2, drained.size());
+    assertEquals(task1, drained.get(0));
+    assertEquals(task2, drained.get(1));
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testIteratorSafeTraversalAndImmutable() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+    queue.offer(task1);
+    queue.offer(task2);
+
+    Iterator<Runnable> it = queue.iterator();
+    assertTrue(it.hasNext());
+    assertEquals(task1, it.next());
+    assertTrue(it.hasNext());
+    assertEquals(task2, it.next());
+    assertFalse(it.hasNext());
+
+    // Assert that mutating the iterator throws UnsupportedOperationException
+    it = queue.iterator();
+    assertTrue(it.hasNext());
+    it.next();
+    try {
+      it.remove();
+      fail("Iterator must be immutable");
+    } catch (UnsupportedOperationException e) {
+      // Expected
+    }
+  }
+
+  @Test
+  public void testPollWorkTargeted() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+
+    QueuedWork workA1 = createQueuedWork("compA", 100);
+    QueuedWork workB1 = createQueuedWork("compB", 200);
+    QueuedWork workA2 = createQueuedWork("compA", 150);
+
+    queue.offer(workA1);
+    queue.offer(workB1);
+    queue.offer(workA2);
+
+    assertEquals(3, queue.size());
+
+    // Targeted poll A
+    QueuedWork polledA1 = queue.pollWork("compA", TEST_KEY_GROUP);
+    assertNotNull(polledA1);
+    assertEquals("compA", polledA1.getWork().getComputationId());
+    assertEquals(100, polledA1.getHandle().bytes());
+
+    // Verify size decremented
+    assertEquals(2, queue.size());
+
+    // Poll next should be B1 (since A1 was stolen, B1 is now first global)
+    assertEquals(workB1, queue.poll());
+    assertEquals(1, queue.size());
+
+    // Last should be A2
+    assertEquals(workA2, queue.poll());
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testMemoryPruningLeavesZeroLeaks() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    QueuedWork workA1 = createQueuedWork("compA", 100);
+    queue.offer(workA1);
+
+    // Steal A1
+    QueuedWork polled = queue.pollWork("compA", TEST_KEY_GROUP);
+    assertNotNull(polled);
+    assertTrue(queue.isEmpty());
+
+    // Offering another work with different computation ID
+    QueuedWork workB1 = createQueuedWork("compB", 200);
+    queue.offer(workB1);
+    assertEquals(1, queue.size());
+
+    // Steal B1
+    QueuedWork polledB = queue.pollWork("compB", TEST_KEY_GROUP);
+    assertNotNull(polledB);
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testConcurrentStress() throws InterruptedException, 
ExecutionException {
+    final KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    final int producerThreads = 4;
+    final int consumerThreads = 4;
+    final int tasksPerProducer = 1000;
+    final int totalTasks = producerThreads * tasksPerProducer;
+
+    ExecutorService executorService =
+        Executors.newFixedThreadPool(producerThreads + consumerThreads);
+    final CountDownLatch startLatch = new CountDownLatch(1);
+    final CountDownLatch doneLatch = new CountDownLatch(producerThreads + 
consumerThreads);
+    final AtomicInteger consumedCount = new AtomicInteger(0);
+    List<Future<?>> futures = new ArrayList<>();
+
+    // Start producers
+    for (int i = 0; i < producerThreads; i++) {
+      futures.add(
+          executorService.submit(
+              () -> {
+                try {
+                  startLatch.await();
+                  for (int j = 0; j < tasksPerProducer; j++) {
+                    String compId = "comp-" + (j % 5);
+                    queue.offer(createQueuedWork(compId, 10));
+                  }
+                } catch (Exception e) {
+                  throw new RuntimeException(e);
+                } finally {
+                  doneLatch.countDown();
+                }
+              }));
+    }
+
+    // Start consumers (mix of poll and pollWork)
+    for (int i = 0; i < consumerThreads; i++) {
+      final int consumerId = i;
+      futures.add(
+          executorService.submit(
+              () -> {
+                try {
+                  startLatch.await();
+                  while (consumedCount.get() < totalTasks) {
+                    Runnable task;
+                    if (consumerId % 2 == 0) {
+                      // Targeted poll
+                      String compId = "comp-" + (consumedCount.get() % 5);
+                      task = queue.pollWork(compId, TEST_KEY_GROUP);
+                    } else {
+                      // Global poll
+                      task = queue.poll();
+                    }
+                    if (task != null) {
+                      consumedCount.incrementAndGet();
+                    }
+                  }
+                } catch (Exception e) {
+                  throw new RuntimeException(e);
+                } finally {
+                  doneLatch.countDown();
+                }
+              }));
+    }
+
+    startLatch.countDown();
+    assertTrue(doneLatch.await(10, TimeUnit.SECONDS));
+
+    // Check for exceptions in threads
+    for (Future<?> future : futures) {
+      future.get();
+    }
+
+    executorService.shutdown();
+    assertTrue(executorService.awaitTermination(5, TimeUnit.SECONDS));
+
+    assertEquals(0, queue.size());
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testTakeBlocksAndWakesUp() throws InterruptedException {
+    final KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    final MockRunnable task = new MockRunnable("take-task");
+    final AtomicReference<Runnable> result = new AtomicReference<>();
+    final CountDownLatch started = new CountDownLatch(1);
+    final CountDownLatch finished = new CountDownLatch(1);
+
+    Thread t =
+        new Thread(
+            () -> {
+              started.countDown();
+              try {
+                result.set(queue.take());
+              } catch (InterruptedException e) {
+                // Ignore
+              } finally {
+                finished.countDown();
+              }
+            });
+    t.setDaemon(true);
+    t.start();
+
+    assertTrue(started.await(2, TimeUnit.SECONDS));
+    // Give thread a moment to enter await()
+    Thread.sleep(100);
+    assertEquals(Thread.State.WAITING, t.getState());

Review Comment:
   instead of sleep and then check, how about a loop while it is not in WAITING
   
   ditto below



##########
runners/google-cloud-dataflow-java/worker/src/test/java/org/apache/beam/runners/dataflow/worker/util/KeyGroupWorkQueueTest.java:
##########
@@ -0,0 +1,473 @@
+/*
+ * 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.beam.runners.dataflow.worker.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+import static org.mockito.Mockito.mock;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
+import org.apache.beam.runners.dataflow.worker.streaming.ExecutableWork;
+import org.apache.beam.runners.dataflow.worker.streaming.Watermarks;
+import org.apache.beam.runners.dataflow.worker.streaming.Work;
+import 
org.apache.beam.runners.dataflow.worker.util.BoundedQueueExecutor.QueuedWork;
+import org.apache.beam.runners.dataflow.worker.windmill.Windmill.WorkItem;
+import 
org.apache.beam.runners.dataflow.worker.windmill.client.getdata.FakeGetDataClient;
+import 
org.apache.beam.runners.dataflow.worker.windmill.work.refresh.HeartbeatSender;
+import org.apache.beam.vendor.grpc.v1p69p0.com.google.protobuf.ByteString;
+import 
org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.util.concurrent.ThreadFactoryBuilder;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.joda.time.Instant;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameters;
+
+@RunWith(Parameterized.class)
+public class KeyGroupWorkQueueTest {
+
+  @Parameters(name = "fairQueue={0}")
+  public static Iterable<Object[]> data() {
+    return Arrays.asList(new Object[][] {{true}, {false}});
+  }
+
+  @Parameterized.Parameter public boolean fairQueue;
+
+  private BoundedQueueExecutor executor;
+
+  @Before
+  public void setUp() {
+    executor =
+        new BoundedQueueExecutor(
+            2,
+            60,
+            TimeUnit.SECONDS,
+            100,
+            10000000,
+            new 
ThreadFactoryBuilder().setNameFormat("Test-%d").setDaemon(true).build(),
+            fairQueue,
+            /*useKeyGroupWorkQueue=*/ true);
+  }
+
+  private static final Work.KeyGroup TEST_KEY_GROUP = Work.KeyGroup.create(1, 
2);
+
+  private QueuedWork createQueuedWork(String computationId, long workBytes) {
+    return createQueuedWork(computationId, TEST_KEY_GROUP, workBytes);
+  }
+
+  private QueuedWork createQueuedWork(
+      String computationId, Work.@Nullable KeyGroup keyGroup, long workBytes) {
+    WorkItem.Builder workItemBuilder =
+        WorkItem.newBuilder()
+            .setKey(ByteString.EMPTY)
+            .setShardingKey(1)
+            .setWorkToken(33)
+            .setCacheToken(1);
+    if (keyGroup != null) {
+      workItemBuilder.setKeyGroup(
+          
org.apache.beam.runners.dataflow.worker.windmill.Windmill.Uint128Proto.newBuilder()
+              .setHigh(keyGroup.high())
+              .setLow(keyGroup.low())
+              .build());
+    }
+    WorkItem workItem = workItemBuilder.build();
+    ExecutableWork work =
+        ExecutableWork.create(
+            Work.create(
+                workItem,
+                workItem.getSerializedSize(),
+                
Watermarks.builder().setInputDataWatermark(Instant.now()).build(),
+                Work.createProcessingContext(
+                    computationId,
+                    new FakeGetDataClient(),
+                    ignored -> {},
+                    mock(HeartbeatSender.class)),
+                false,
+                Instant::now),
+            (w, h) -> {});
+    return new QueuedWork(work, executor.createBudgetHandle(1, workBytes));
+  }
+
+  private static class MockRunnable implements Runnable {
+    final String id;
+
+    MockRunnable(String id) {
+      this.id = id;
+    }
+
+    @Override
+    public void run() {}
+
+    @Override
+    public String toString() {
+      return "MockRunnable(" + id + ")";
+    }
+  }
+
+  @Test
+  public void testBasicOfferAndPoll() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    assertTrue(queue.isEmpty());
+    assertEquals(0, queue.size());
+
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+
+    assertTrue(queue.offer(task1));
+    assertTrue(queue.offer(task2));
+    assertEquals(2, queue.size());
+
+    assertEquals(task1, queue.poll());
+    assertEquals(task2, queue.poll());
+    assertNull(queue.poll());
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testRemove() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+
+    queue.offer(task1);
+    queue.offer(task2);
+
+    assertTrue(queue.remove(task1));
+    assertEquals(1, queue.size());
+    assertEquals(task2, queue.poll());
+    assertFalse(queue.remove(task1)); // Already gone
+  }
+
+  @Test
+  public void testDrainTo() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+    queue.offer(task1);
+    queue.offer(task2);
+
+    List<Runnable> drained = new ArrayList<>();
+    assertEquals(2, queue.drainTo(drained));
+    assertEquals(2, drained.size());
+    assertEquals(task1, drained.get(0));
+    assertEquals(task2, drained.get(1));
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testIteratorSafeTraversalAndImmutable() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+    queue.offer(task1);
+    queue.offer(task2);
+
+    Iterator<Runnable> it = queue.iterator();
+    assertTrue(it.hasNext());
+    assertEquals(task1, it.next());
+    assertTrue(it.hasNext());
+    assertEquals(task2, it.next());
+    assertFalse(it.hasNext());
+
+    // Assert that mutating the iterator throws UnsupportedOperationException
+    it = queue.iterator();
+    assertTrue(it.hasNext());
+    it.next();
+    try {
+      it.remove();
+      fail("Iterator must be immutable");
+    } catch (UnsupportedOperationException e) {
+      // Expected
+    }
+  }
+
+  @Test
+  public void testPollWorkTargeted() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+
+    QueuedWork workA1 = createQueuedWork("compA", 100);
+    QueuedWork workB1 = createQueuedWork("compB", 200);
+    QueuedWork workA2 = createQueuedWork("compA", 150);
+
+    queue.offer(workA1);
+    queue.offer(workB1);
+    queue.offer(workA2);
+
+    assertEquals(3, queue.size());
+
+    // Targeted poll A
+    QueuedWork polledA1 = queue.pollWork("compA", TEST_KEY_GROUP);
+    assertNotNull(polledA1);
+    assertEquals("compA", polledA1.getWork().getComputationId());
+    assertEquals(100, polledA1.getHandle().bytes());
+
+    // Verify size decremented
+    assertEquals(2, queue.size());
+
+    // Poll next should be B1 (since A1 was stolen, B1 is now first global)
+    assertEquals(workB1, queue.poll());
+    assertEquals(1, queue.size());
+
+    // Last should be A2
+    assertEquals(workA2, queue.poll());
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testMemoryPruningLeavesZeroLeaks() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    QueuedWork workA1 = createQueuedWork("compA", 100);
+    queue.offer(workA1);
+
+    // Steal A1
+    QueuedWork polled = queue.pollWork("compA", TEST_KEY_GROUP);
+    assertNotNull(polled);
+    assertTrue(queue.isEmpty());
+
+    // Offering another work with different computation ID
+    QueuedWork workB1 = createQueuedWork("compB", 200);
+    queue.offer(workB1);
+    assertEquals(1, queue.size());
+
+    // Steal B1
+    QueuedWork polledB = queue.pollWork("compB", TEST_KEY_GROUP);
+    assertNotNull(polledB);
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testConcurrentStress() throws InterruptedException, 
ExecutionException {
+    final KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    final int producerThreads = 4;
+    final int consumerThreads = 4;
+    final int tasksPerProducer = 1000;
+    final int totalTasks = producerThreads * tasksPerProducer;
+
+    ExecutorService executorService =
+        Executors.newFixedThreadPool(producerThreads + consumerThreads);
+    final CountDownLatch startLatch = new CountDownLatch(1);
+    final CountDownLatch doneLatch = new CountDownLatch(producerThreads + 
consumerThreads);
+    final AtomicInteger consumedCount = new AtomicInteger(0);
+    List<Future<?>> futures = new ArrayList<>();
+
+    // Start producers
+    for (int i = 0; i < producerThreads; i++) {
+      futures.add(
+          executorService.submit(
+              () -> {
+                try {
+                  startLatch.await();
+                  for (int j = 0; j < tasksPerProducer; j++) {
+                    String compId = "comp-" + (j % 5);
+                    queue.offer(createQueuedWork(compId, 10));
+                  }
+                } catch (Exception e) {
+                  throw new RuntimeException(e);
+                } finally {
+                  doneLatch.countDown();
+                }
+              }));
+    }
+
+    // Start consumers (mix of poll and pollWork)
+    for (int i = 0; i < consumerThreads; i++) {
+      final int consumerId = i;
+      futures.add(
+          executorService.submit(
+              () -> {
+                try {
+                  startLatch.await();
+                  while (consumedCount.get() < totalTasks) {
+                    Runnable task;
+                    if (consumerId % 2 == 0) {
+                      // Targeted poll
+                      String compId = "comp-" + (consumedCount.get() % 5);
+                      task = queue.pollWork(compId, TEST_KEY_GROUP);
+                    } else {
+                      // Global poll
+                      task = queue.poll();
+                    }
+                    if (task != null) {
+                      consumedCount.incrementAndGet();
+                    }

Review Comment:
   if task is null, should we perform blocking take the next time?



##########
runners/google-cloud-dataflow-java/worker/src/test/java/org/apache/beam/runners/dataflow/worker/util/KeyGroupWorkQueueTest.java:
##########
@@ -0,0 +1,473 @@
+/*
+ * 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.beam.runners.dataflow.worker.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+import static org.mockito.Mockito.mock;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
+import org.apache.beam.runners.dataflow.worker.streaming.ExecutableWork;
+import org.apache.beam.runners.dataflow.worker.streaming.Watermarks;
+import org.apache.beam.runners.dataflow.worker.streaming.Work;
+import 
org.apache.beam.runners.dataflow.worker.util.BoundedQueueExecutor.QueuedWork;
+import org.apache.beam.runners.dataflow.worker.windmill.Windmill.WorkItem;
+import 
org.apache.beam.runners.dataflow.worker.windmill.client.getdata.FakeGetDataClient;
+import 
org.apache.beam.runners.dataflow.worker.windmill.work.refresh.HeartbeatSender;
+import org.apache.beam.vendor.grpc.v1p69p0.com.google.protobuf.ByteString;
+import 
org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.util.concurrent.ThreadFactoryBuilder;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.joda.time.Instant;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameters;
+
+@RunWith(Parameterized.class)
+public class KeyGroupWorkQueueTest {
+
+  @Parameters(name = "fairQueue={0}")
+  public static Iterable<Object[]> data() {
+    return Arrays.asList(new Object[][] {{true}, {false}});
+  }
+
+  @Parameterized.Parameter public boolean fairQueue;
+
+  private BoundedQueueExecutor executor;
+
+  @Before
+  public void setUp() {
+    executor =
+        new BoundedQueueExecutor(
+            2,
+            60,
+            TimeUnit.SECONDS,
+            100,
+            10000000,
+            new 
ThreadFactoryBuilder().setNameFormat("Test-%d").setDaemon(true).build(),
+            fairQueue,
+            /*useKeyGroupWorkQueue=*/ true);
+  }
+
+  private static final Work.KeyGroup TEST_KEY_GROUP = Work.KeyGroup.create(1, 
2);
+
+  private QueuedWork createQueuedWork(String computationId, long workBytes) {
+    return createQueuedWork(computationId, TEST_KEY_GROUP, workBytes);
+  }
+
+  private QueuedWork createQueuedWork(
+      String computationId, Work.@Nullable KeyGroup keyGroup, long workBytes) {
+    WorkItem.Builder workItemBuilder =
+        WorkItem.newBuilder()
+            .setKey(ByteString.EMPTY)
+            .setShardingKey(1)
+            .setWorkToken(33)
+            .setCacheToken(1);
+    if (keyGroup != null) {
+      workItemBuilder.setKeyGroup(
+          
org.apache.beam.runners.dataflow.worker.windmill.Windmill.Uint128Proto.newBuilder()
+              .setHigh(keyGroup.high())
+              .setLow(keyGroup.low())
+              .build());
+    }
+    WorkItem workItem = workItemBuilder.build();
+    ExecutableWork work =
+        ExecutableWork.create(
+            Work.create(
+                workItem,
+                workItem.getSerializedSize(),
+                
Watermarks.builder().setInputDataWatermark(Instant.now()).build(),
+                Work.createProcessingContext(
+                    computationId,
+                    new FakeGetDataClient(),
+                    ignored -> {},
+                    mock(HeartbeatSender.class)),
+                false,
+                Instant::now),
+            (w, h) -> {});
+    return new QueuedWork(work, executor.createBudgetHandle(1, workBytes));
+  }
+
+  private static class MockRunnable implements Runnable {
+    final String id;
+
+    MockRunnable(String id) {
+      this.id = id;
+    }
+
+    @Override
+    public void run() {}
+
+    @Override
+    public String toString() {
+      return "MockRunnable(" + id + ")";
+    }
+  }
+
+  @Test
+  public void testBasicOfferAndPoll() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    assertTrue(queue.isEmpty());
+    assertEquals(0, queue.size());
+
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+
+    assertTrue(queue.offer(task1));
+    assertTrue(queue.offer(task2));
+    assertEquals(2, queue.size());
+
+    assertEquals(task1, queue.poll());
+    assertEquals(task2, queue.poll());
+    assertNull(queue.poll());
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testRemove() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+
+    queue.offer(task1);
+    queue.offer(task2);
+
+    assertTrue(queue.remove(task1));
+    assertEquals(1, queue.size());
+    assertEquals(task2, queue.poll());
+    assertFalse(queue.remove(task1)); // Already gone
+  }
+
+  @Test
+  public void testDrainTo() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+    queue.offer(task1);
+    queue.offer(task2);
+
+    List<Runnable> drained = new ArrayList<>();
+    assertEquals(2, queue.drainTo(drained));
+    assertEquals(2, drained.size());
+    assertEquals(task1, drained.get(0));
+    assertEquals(task2, drained.get(1));
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testIteratorSafeTraversalAndImmutable() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    MockRunnable task1 = new MockRunnable("1");
+    MockRunnable task2 = new MockRunnable("2");
+    queue.offer(task1);
+    queue.offer(task2);
+
+    Iterator<Runnable> it = queue.iterator();
+    assertTrue(it.hasNext());
+    assertEquals(task1, it.next());
+    assertTrue(it.hasNext());
+    assertEquals(task2, it.next());
+    assertFalse(it.hasNext());
+
+    // Assert that mutating the iterator throws UnsupportedOperationException
+    it = queue.iterator();
+    assertTrue(it.hasNext());
+    it.next();
+    try {
+      it.remove();
+      fail("Iterator must be immutable");
+    } catch (UnsupportedOperationException e) {
+      // Expected
+    }
+  }
+
+  @Test
+  public void testPollWorkTargeted() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+
+    QueuedWork workA1 = createQueuedWork("compA", 100);
+    QueuedWork workB1 = createQueuedWork("compB", 200);
+    QueuedWork workA2 = createQueuedWork("compA", 150);
+
+    queue.offer(workA1);
+    queue.offer(workB1);
+    queue.offer(workA2);
+
+    assertEquals(3, queue.size());
+
+    // Targeted poll A
+    QueuedWork polledA1 = queue.pollWork("compA", TEST_KEY_GROUP);
+    assertNotNull(polledA1);
+    assertEquals("compA", polledA1.getWork().getComputationId());
+    assertEquals(100, polledA1.getHandle().bytes());
+
+    // Verify size decremented
+    assertEquals(2, queue.size());
+
+    // Poll next should be B1 (since A1 was stolen, B1 is now first global)
+    assertEquals(workB1, queue.poll());
+    assertEquals(1, queue.size());
+
+    // Last should be A2
+    assertEquals(workA2, queue.poll());
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testMemoryPruningLeavesZeroLeaks() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    QueuedWork workA1 = createQueuedWork("compA", 100);
+    queue.offer(workA1);
+
+    // Steal A1
+    QueuedWork polled = queue.pollWork("compA", TEST_KEY_GROUP);
+    assertNotNull(polled);
+    assertTrue(queue.isEmpty());
+
+    // Offering another work with different computation ID
+    QueuedWork workB1 = createQueuedWork("compB", 200);
+    queue.offer(workB1);
+    assertEquals(1, queue.size());
+
+    // Steal B1
+    QueuedWork polledB = queue.pollWork("compB", TEST_KEY_GROUP);
+    assertNotNull(polledB);
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testConcurrentStress() throws InterruptedException, 
ExecutionException {
+    final KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    final int producerThreads = 4;
+    final int consumerThreads = 4;
+    final int tasksPerProducer = 1000;
+    final int totalTasks = producerThreads * tasksPerProducer;
+
+    ExecutorService executorService =
+        Executors.newFixedThreadPool(producerThreads + consumerThreads);
+    final CountDownLatch startLatch = new CountDownLatch(1);
+    final CountDownLatch doneLatch = new CountDownLatch(producerThreads + 
consumerThreads);
+    final AtomicInteger consumedCount = new AtomicInteger(0);
+    List<Future<?>> futures = new ArrayList<>();
+
+    // Start producers
+    for (int i = 0; i < producerThreads; i++) {
+      futures.add(
+          executorService.submit(
+              () -> {
+                try {
+                  startLatch.await();
+                  for (int j = 0; j < tasksPerProducer; j++) {
+                    String compId = "comp-" + (j % 5);
+                    queue.offer(createQueuedWork(compId, 10));
+                  }
+                } catch (Exception e) {
+                  throw new RuntimeException(e);
+                } finally {
+                  doneLatch.countDown();
+                }
+              }));
+    }
+
+    // Start consumers (mix of poll and pollWork)
+    for (int i = 0; i < consumerThreads; i++) {
+      final int consumerId = i;
+      futures.add(
+          executorService.submit(
+              () -> {
+                try {
+                  startLatch.await();
+                  while (consumedCount.get() < totalTasks) {
+                    Runnable task;
+                    if (consumerId % 2 == 0) {
+                      // Targeted poll
+                      String compId = "comp-" + (consumedCount.get() % 5);
+                      task = queue.pollWork(compId, TEST_KEY_GROUP);
+                    } else {
+                      // Global poll
+                      task = queue.poll();
+                    }
+                    if (task != null) {
+                      consumedCount.incrementAndGet();
+                    }
+                  }
+                } catch (Exception e) {
+                  throw new RuntimeException(e);
+                } finally {
+                  doneLatch.countDown();
+                }
+              }));
+    }
+
+    startLatch.countDown();
+    assertTrue(doneLatch.await(10, TimeUnit.SECONDS));
+
+    // Check for exceptions in threads
+    for (Future<?> future : futures) {
+      future.get();
+    }
+
+    executorService.shutdown();
+    assertTrue(executorService.awaitTermination(5, TimeUnit.SECONDS));
+
+    assertEquals(0, queue.size());
+    assertTrue(queue.isEmpty());
+  }
+
+  @Test
+  public void testTakeBlocksAndWakesUp() throws InterruptedException {
+    final KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    final MockRunnable task = new MockRunnable("take-task");
+    final AtomicReference<Runnable> result = new AtomicReference<>();
+    final CountDownLatch started = new CountDownLatch(1);
+    final CountDownLatch finished = new CountDownLatch(1);
+
+    Thread t =
+        new Thread(
+            () -> {
+              started.countDown();
+              try {
+                result.set(queue.take());
+              } catch (InterruptedException e) {
+                // Ignore
+              } finally {
+                finished.countDown();
+              }
+            });
+    t.setDaemon(true);
+    t.start();
+
+    assertTrue(started.await(2, TimeUnit.SECONDS));
+    // Give thread a moment to enter await()
+    Thread.sleep(100);
+    assertEquals(Thread.State.WAITING, t.getState());
+
+    queue.offer(task);
+
+    assertTrue(finished.await(2, TimeUnit.SECONDS));
+    assertEquals(task, result.get());
+  }
+
+  @Test
+  public void testPollWithTimeout() throws InterruptedException {
+    final KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+    final MockRunnable task = new MockRunnable("poll-task");
+    final AtomicReference<Runnable> result = new AtomicReference<>();
+    final CountDownLatch started = new CountDownLatch(1);
+    final CountDownLatch finished = new CountDownLatch(1);
+
+    // 1. Verify timeout returns null
+    Thread t1 =
+        new Thread(
+            () -> {
+              started.countDown();
+              try {
+                result.set(queue.poll(500, TimeUnit.MILLISECONDS));
+              } catch (InterruptedException e) {
+                // Ignore
+              } finally {
+                finished.countDown();
+              }
+            });
+    t1.setDaemon(true);
+    t1.start();
+
+    assertTrue(started.await(2, TimeUnit.SECONDS));
+    Thread.sleep(100);
+    assertEquals(Thread.State.TIMED_WAITING, t1.getState());
+
+    assertTrue(finished.await(2, TimeUnit.SECONDS));
+    assertNull(result.get());
+
+    // 2. Verify timed poll receives task offered concurrently
+    final CountDownLatch started2 = new CountDownLatch(1);
+    final CountDownLatch finished2 = new CountDownLatch(1);
+    final AtomicReference<Runnable> result2 = new AtomicReference<>();
+
+    Thread t2 =
+        new Thread(
+            () -> {
+              started2.countDown();
+              try {
+                result2.set(queue.poll(2, TimeUnit.SECONDS));
+              } catch (InterruptedException e) {
+                // Ignore
+              } finally {
+                finished2.countDown();
+              }
+            });
+    t2.setDaemon(true);
+    t2.start();
+
+    assertTrue(started2.await(2, TimeUnit.SECONDS));
+    Thread.sleep(100);
+    assertEquals(Thread.State.TIMED_WAITING, t2.getState());
+
+    queue.offer(task);
+
+    assertTrue(finished2.await(2, TimeUnit.SECONDS));
+    assertEquals(task, result2.get());
+  }
+
+  @Test
+  public void testPollWorkWithKeyGroup() {
+    KeyGroupWorkQueue queue = new KeyGroupWorkQueue(fairQueue);
+
+    Work.KeyGroup keyGroup1 = Work.KeyGroup.create(1, 1);
+    Work.KeyGroup keyGroup2 = Work.KeyGroup.create(1, 2);
+
+    QueuedWork workA1 = createQueuedWork("compA", keyGroup1, 100);
+    QueuedWork workA2 = createQueuedWork("compA", keyGroup2, 150);
+
+    queue.offer(workA1);
+    queue.offer(workA2);
+
+    assertEquals(2, queue.size());
+
+    // Poll with keyGroup2 first - should return workA2
+    QueuedWork polledA2 = queue.pollWork("compA", keyGroup2);
+    assertNotNull(polledA2);
+    assertEquals(workA2, polledA2);
+    assertEquals(1, queue.size());
+
+    // Poll with keyGroup2 again - should return null

Review Comment:
   trying polling a keygroup never added



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