[Java Client] Improve consumer listener logic (#13273)

* [Java Client] Improve consumer listener logic

* Move isListenerHandlingMessage update to before submitting to executor

(cherry picked from commit 9f46c4a)

pulsar-client/src/main/java/org/apache/pulsar/client/impl/ConsumerBase.java

@@ -34,7 +34,6 @@
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;
-import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicLongFieldUpdater;
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
@@ -85,7 +84,7 @@ public abstract class ConsumerBase<T> extends HandlerState implements Consumer<T
     protected volatile long incomingMessagesSize = 0;
     protected volatile Timeout batchReceiveTimeout = null;
     protected final Lock reentrantLock = new ReentrantLock();
-    private final AtomicInteger executorQueueSize = new AtomicInteger(0);
+    private volatile boolean isListenerHandlingMessage = false;
 
     protected ConsumerBase(PulsarClientImpl client, String topic, ConsumerConfigurationData<T> conf,
                            int receiverQueueSize, ExecutorProvider executorProvider,
@@ -908,15 +907,17 @@ private void doPendingBatchReceiveTask(Timeout timeout) {
     }
 
     protected void triggerListener() {
-        // Trigger the notification on the message listener in a separate thread to avoid blocking the networking
-        // thread while the message processing happens
+        // Use internalPinnedExecutor to maintain message ordering
         internalPinnedExecutor.execute(() -> {
             try {
-                // Control executor to call MessageListener one by one.
-                if (executorQueueSize.get() < 1) {
+                // Listener should only have one pending/running executable to process a message
+                // See https://github.com/apache/pulsar/issues/11008 for context.
+                if (!isListenerHandlingMessage) {
                     final Message<T> msg = internalReceive(0, TimeUnit.MILLISECONDS);
                     if (msg != null) {
-                        executorQueueSize.incrementAndGet();
+                        isListenerHandlingMessage = true;
+                        // Trigger the notification on the message listener in a separate thread to avoid blocking the
+                        // internal pinned executor thread while the message processing happens
                         if (SubscriptionType.Key_Shared == conf.getSubscriptionType()) {
                             executorProvider.getExecutor(peekMessageKey(msg)).execute(() ->
                                     callMessageListener(msg));
@@ -949,7 +950,7 @@ protected void callMessageListener(Message<T> msg) {
             log.error("[{}][{}] Message listener error in processing message: {}", topic, subscription,
                     msg.getMessageId(), t);
         } finally {
-            executorQueueSize.decrementAndGet();
+            isListenerHandlingMessage = false;
             triggerListener();
         }
     }