[fix][broker] Continue closing even when executor is shut down (apache#22599)

Author: lhotari

pulsar-broker/src/main/java/org/apache/pulsar/broker/service/persistent/PersistentTopic.java

@@ -45,6 +45,7 @@
 import java.util.concurrent.CompletionException;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
+import java.util.concurrent.RejectedExecutionException;
 import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
@@ -1429,7 +1430,14 @@ private CompletableFuture<Void> delete(boolean failIfHasSubscriptions,
                 }
                 FutureUtil.waitForAll(futures).thenRunAsync(() -> {
                     closeClientFuture.complete(null);
-                }, getOrderedExecutor()).exceptionally(ex -> {
+                }, command -> {
+                    try {
+                        getOrderedExecutor().execute(command);
+                    } catch (RejectedExecutionException e) {
+                        // executor has been shut down, execute in current thread
+                        command.run();
+                    }
+                }).exceptionally(ex -> {
                     log.error("[{}] Error closing clients", topic, ex);
                     unfenceTopicToResume();
                     closeClientFuture.completeExceptionally(ex);