Implement heartbeat on timer to keep visualizer alive (#1463)

* implement heartbeat on timer to keep visualizer alive

* heartbeat every second

* Update VisWebSocket.java

Remove debugging line

* Update CHANGELOG.md

Fix issue 523, use version 4.5 in changelog since there's no 4.4.1 public distro

CHANGELOG.md

@@ -4,13 +4,14 @@ GitHub issues or pull requests that
 are related to the items below. If there is no issue or pull
 request related to the change, then we may provide the commit.
 
-v4.4.1
+v4.5
 ======
 - Fix issue [#1378](https://github.com/opensim-org/opensim-gui/issues/1378): In Static Optimization Tool, dialog box has wrong title for "Directory" in output section.
 - Fix issue [#1395](https://github.com/opensim-org/opensim-gui/issues/1395): Where visual selection and properties windows are not in sync.
 - Fix issue [#1357](https://github.com/opensim-org/opensim-gui/issues/1357): Toolbar displaced and non visible after resizing window
 - Fix issue [#1416](https://github.com/opensim-org/opensim-gui/issues/1416): Remove visual offset added to experimental data in "Preview Experimnetal Data".
 - Fix issue [#1426](https://github.com/opensim-org/opensim-gui/issues/1426): Make graphical selection of pathpoints and markers more robust among overlapping objects.
+- Fix issue [#523](https://github.com/opensim-org/opensim-gui/issues/523): Keep visualizer alive through arbitrary long idle time.
 
 v4.4
 ====

Gui/opensim/visualizationServer/src/org/eclipse/jetty/MyWebSocketHandler.java

@@ -29,6 +29,10 @@
 package org.eclipse.jetty;
 
 import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
 import org.eclipse.jetty.websocket.api.Session;
 import org.eclipse.jetty.websocket.api.annotations.OnWebSocketClose;
 import org.eclipse.jetty.websocket.api.annotations.OnWebSocketConnect;
@@ -43,6 +47,8 @@
 @WebSocket
 public class MyWebSocketHandler {
 
+    private final ScheduledExecutorService executorService = Executors.newScheduledThreadPool(1);
+
     @OnWebSocketClose
     public void onClose(int statusCode, String reason) {
         System.out.println("Close: statusCode=" + statusCode + ", reason=" + reason);
@@ -55,6 +61,16 @@ public void onError(Throwable t) {
 
     @OnWebSocketConnect
     public void onConnect(Session session) {
+        executorService.scheduleAtFixedRate(() -> {
+                    try {
+                        String data = "Ping";
+                        ByteBuffer payload = ByteBuffer.wrap(data.getBytes());
+                        session.getRemote().sendPing(payload);
+                    } catch (IOException e) {
+                        e.printStackTrace();
+                    }
+                },
+                5, 5, TimeUnit.MINUTES);
         System.out.println("Connect: " + session.getRemoteAddress().getAddress());
         try {
             session.getRemote().sendString("Hello Webbrowser");

Gui/opensim/visualizationServer/src/org/eclipse/jetty/VisWebSocket.java

@@ -28,10 +28,14 @@
 package org.eclipse.jetty;
 
 import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Observable;
 import java.util.Set;
+import java.util.concurrent.TimeUnit;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 import org.eclipse.jetty.websocket.api.Session;
@@ -52,6 +56,7 @@
 @WebSocket(maxTextMessageSize = 64 * 4096, maxIdleTime=10000000)
 public class VisWebSocket extends Observable { // Socket to handle incoming traffic from Browser
     private static final Set<Session> peers = Collections.synchronizedSet(new HashSet<Session>());
+    private final ScheduledExecutorService executorService = Executors.newScheduledThreadPool(1);
 
     public VisWebSocket(){
         // Register socket with WebSocketDB so it can be called back
@@ -66,7 +71,17 @@ public void onOpen (Session peer) {
             this.setChanged();
             this.notifyObservers();
         }
-
+        executorService.scheduleAtFixedRate(() -> {
+                    try {
+                        String data = "Ping";
+                        ByteBuffer payload = ByteBuffer.wrap(data.getBytes());
+                        peer.getRemote().sendPing(payload);
+                        //System.out.println("Sending ping to peer.");
+                    } catch (IOException e) {
+                        e.printStackTrace();
+                    }
+                },
+                1, 1, TimeUnit.MINUTES);        
 
     }