Clean up the EventService class used for gRPC tests and add comments …

…to explain what it does.

nima/tests/integration/grpc/server/src/main/java/io/helidon/nima/tests/integration/grpc/webserver/EventService.java

@@ -18,6 +18,7 @@
 
 import java.util.ArrayList;
 import java.util.HashSet;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Set;
 import java.util.concurrent.locks.Lock;
@@ -32,10 +33,23 @@
 
 import static io.helidon.nima.grpc.webserver.ResponseHelper.complete;
 
+/**
+ * A simple service to send events to subscriber listeners.
+ * <p/>
+ * The main purpose of this service it so test long-running bidirectional
+ * gRPC requests alongside concurrent unary requests so that there are
+ * multiple in-flight requests at the same time on the same gRPC channel.
+ */
 public class EventService implements GrpcService {
 
+    /**
+     * The registered listeners.
+     */
     private final List<Listener> listeners = new ArrayList<>();
 
+    /**
+     * A lock to control mutating the listeners list.
+     */
     private final Lock lock = new ReentrantLock();
 
     @Override
@@ -49,6 +63,16 @@ public void update(Routing router) {
                 .bidi("Events", this::events);
     }
 
+    /**
+     * The events bidirectional request.
+     * <p/>
+     * Clients send subscribe or un-subscribe requests up the channel, and the server
+     * sends events back down the channel.
+     *
+     * @param responses  the {@link StreamObserver} to receive event responses
+     *
+     * @return the {@link StreamObserver} to receive subscription requests
+     */
     private StreamObserver<Events.EventRequest> events(StreamObserver<Events.EventResponse> responses) {
         lock.lock();
         try {
@@ -60,27 +84,58 @@ private StreamObserver<Events.EventRequest> events(StreamObserver<Events.EventRe
         }
     }
 
+    /**
+     * Send an event to all subscribed listeners.
+     *
+     * @param message   the message to send
+     * @param observer  the observer that is completed when events have been sent
+     */
     private void send(Events.Message message, StreamObserver<Empty> observer) {
         String text = message.getText();
-        for (Listener listener : listeners) {
+        Iterator<Listener> it = listeners.iterator();
+        while (it.hasNext()) {
+            Listener listener = it.next();
             listener.send(text);
         }
         complete(observer, Empty.getDefaultInstance());
     }
 
+    /**
+     * An implementation of a {@link StreamObserver} used to
+     * subscribe or unsubscribe listeners for a specific
+     * bidirectional channel.
+     */
     private class Listener
         implements StreamObserver<Events.EventRequest> {
 
+        /**
+         * The {@link StreamObserver} to send events to.
+         */
         private final StreamObserver<Events.EventResponse> responses;
 
+        /**
+         * The set of subscriber identifiers.
+         */
         private final Set<Long> subscribers = new HashSet<>();
 
+        /**
+         * Create a Listener.
+         *
+         * @param responses {@link StreamObserver} to send events to
+         */
         public Listener(StreamObserver<Events.EventResponse> responses) {
             this.responses = responses;
         }
 
+        /**
+         * Send an event to all subscribers.
+         *
+         * @param text the message to send
+         */
         public void send(String text) {
-            for (long id : subscribers) {
+            Iterator<Long> it = subscribers.iterator();
+            while(it.hasNext()) {
+                long id = it.next();
                 responses.onNext(Events.EventResponse.newBuilder()
                                          .setEvent(Events.Event.newBuilder()
                                                            .setId(id)
@@ -89,6 +144,14 @@ public void send(String text) {
             }
         }
 
+        /**
+         * Handle messages from the client to subscribe or
+         * unsubscribe. Listeners are just registered by
+         * keeping an ID and events are sent to for each
+         * subscribed ID.
+         *
+         * @param request a request to subscribe or unsubscribe
+         */
         @Override
         public void onNext(Events.EventRequest request) {
             long id = request.getId();