HDDS-513. Check if the EventQueue is not closed before executing handlers. Contributed by Nanda Kumar.

hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/server/events/EventQueue.java

@@ -55,6 +55,8 @@ public class EventQueue implements EventPublisher, AutoCloseable {
 
   private final AtomicLong eventCount = new AtomicLong(0);
 
+  private boolean isRunning = true;
+
   public <PAYLOAD, EVENT_TYPE extends Event<PAYLOAD>> void addHandler(
       EVENT_TYPE event, EventHandler<PAYLOAD> handler) {
     this.addHandler(event, handler, generateHandlerName(handler));
@@ -116,6 +118,10 @@ public class EventQueue implements EventPublisher, AutoCloseable {
   public <PAYLOAD, EVENT_TYPE extends Event<PAYLOAD>> void addHandler(
       EVENT_TYPE event, EventExecutor<PAYLOAD> executor,
       EventHandler<PAYLOAD> handler) {
+    if (!isRunning) {
+      LOG.warn("Not adding handler for {}, EventQueue is not running", event);
+      return;
+    }
     validateEvent(event);
     executors.putIfAbsent(event, new HashMap<>());
     executors.get(event).putIfAbsent(executor, new ArrayList<>());
@@ -136,6 +142,11 @@ public class EventQueue implements EventPublisher, AutoCloseable {
   public <PAYLOAD, EVENT_TYPE extends Event<PAYLOAD>> void fireEvent(
       EVENT_TYPE event, PAYLOAD payload) {
 
+    if (!isRunning) {
+      LOG.warn("Processing of {} is skipped, EventQueue is not running", event);
+      return;
+    }
+
     Map<EventExecutor, List<EventHandler>> eventExecutorListMap =
         this.executors.get(event);
 
@@ -187,6 +198,11 @@ public class EventQueue implements EventPublisher, AutoCloseable {
     long currentTime = Time.now();
     while (true) {
 
+      if (!isRunning) {
+        LOG.warn("Processing of event skipped. EventQueue is not running");
+        return;
+      }
+
       long processed = 0;
 
       Stream<EventExecutor> allExecutor = this.executors.values().stream()
@@ -216,6 +232,8 @@ public class EventQueue implements EventPublisher, AutoCloseable {
 
   public void close() {
 
+    isRunning = false;
+
     Set<EventExecutor> allExecutors = this.executors.values().stream()
         .flatMap(handlerMap -> handlerMap.keySet().stream())
         .collect(Collectors.toSet());