KAFKA-15305: The background thread should try to process the remaining task until the shutdown timer is expired.

clients/src/main/java/org/apache/kafka/clients/consumer/internals/ConsumerNetworkThread.java

@@ -293,12 +293,13 @@ private void closeInternal(final Duration timeout) {
      * Check the unsent queue one last time and poll until all requests are sent or the timer runs out.
      */
     private void sendUnsentRequests(final Timer timer) {
-        if (networkClientDelegate.unsentRequests().isEmpty())
+        if (!networkClientDelegate.hasAnyPendingRequests())
             return;
+
         do {
             networkClientDelegate.poll(timer.remainingMs(), timer.currentTimeMs());
             timer.update();
-        } while (timer.notExpired() && !networkClientDelegate.unsentRequests().isEmpty());
+        } while (timer.notExpired() && networkClientDelegate.hasAnyPendingRequests());
     }
 
     void cleanup() {

clients/src/main/java/org/apache/kafka/clients/consumer/internals/NetworkClientDelegate.java

@@ -130,6 +130,13 @@ public void poll(final long timeoutMs, final long currentTimeMs) {
         checkDisconnects(currentTimeMs);
     }
 
+    /**
+     * Return true if there is at least one in-flight request or unsent request.
+     */
+    public boolean hasAnyPendingRequests() {
+        return client.hasInFlightRequests() || !unsentRequests.isEmpty();
+    }
+
     /**
      * Tries to send the requests in the unsentRequest queue. If the request doesn't have an assigned node, it will
      * find the leastLoadedOne, and will be retried in the next {@code poll()}. If the request is expired, a

clients/src/test/java/org/apache/kafka/clients/consumer/internals/ConsumerNetworkThreadTest.java

@@ -339,6 +339,27 @@ void testRunOnceInvokesReaper() {
         verify(applicationEventReaper).reap(any(Long.class));
     }
 
+    @Test
+    void testSendUnsentRequest() {
+        String groupId = "group-id";
+        NetworkClientDelegate.UnsentRequest request = new NetworkClientDelegate.UnsentRequest(
+            new FindCoordinatorRequest.Builder(
+                new FindCoordinatorRequestData()
+                    .setKeyType(FindCoordinatorRequest.CoordinatorType.TRANSACTION.id())
+                    .setKey(groupId)),
+            Optional.empty());
+
+        networkClient.add(request);
+        assertTrue(networkClient.hasAnyPendingRequests());
+        assertFalse(networkClient.unsentRequests().isEmpty());
+        assertFalse(client.hasInFlightRequests());
+        consumerNetworkThread.cleanup();
+
+        assertTrue(networkClient.unsentRequests().isEmpty());
+        assertFalse(client.hasInFlightRequests());
+        assertFalse(networkClient.hasAnyPendingRequests());
+    }
+
     private void prepareOffsetCommitRequest(final Map<TopicPartition, Long> expectedOffsets,
                                             final Errors error,
                                             final boolean disconnected) {

clients/src/test/java/org/apache/kafka/clients/consumer/internals/NetworkClientDelegateTest.java

@@ -43,6 +43,7 @@
 import static org.apache.kafka.clients.consumer.ConsumerConfig.REQUEST_TIMEOUT_MS_CONFIG;
 import static org.apache.kafka.clients.consumer.ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG;
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -140,6 +141,34 @@ public void testEnsureTimerSetOnAdd() {
         assertEquals(REQUEST_TIMEOUT_MS, ncd.unsentRequests().poll().timer().timeoutMs());
     }
 
+    @Test
+    public void testHasAnyPendingRequests() throws Exception {
+        try (NetworkClientDelegate networkClientDelegate = newNetworkClientDelegate()) {
+            NetworkClientDelegate.UnsentRequest unsentRequest = newUnsentFindCoordinatorRequest();
+            networkClientDelegate.add(unsentRequest);
+
+            // unsent
+            assertTrue(networkClientDelegate.hasAnyPendingRequests());
+            assertFalse(networkClientDelegate.unsentRequests().isEmpty());
+            assertFalse(client.hasInFlightRequests());
+
+            networkClientDelegate.poll(0, time.milliseconds());
+
+            // in-flight
+            assertTrue(networkClientDelegate.hasAnyPendingRequests());
+            assertTrue(networkClientDelegate.unsentRequests().isEmpty());
+            assertTrue(client.hasInFlightRequests());
+
+            client.respond(FindCoordinatorResponse.prepareResponse(Errors.NONE, GROUP_ID, mockNode()));
+            networkClientDelegate.poll(0, time.milliseconds());
+
+            // get response
+            assertFalse(networkClientDelegate.hasAnyPendingRequests());
+            assertTrue(networkClientDelegate.unsentRequests().isEmpty());
+            assertFalse(client.hasInFlightRequests());
+        }
+    }
+
     public NetworkClientDelegate newNetworkClientDelegate() {
         LogContext logContext = new LogContext();
         Properties properties = new Properties();