hard reference JmxModel so we are sure that it is not garbage collected

Author: thurka

visualvm/jmx/src/org/graalvm/visualvm/jmx/impl/JmxApplication.java

@@ -56,6 +56,7 @@ public final class JmxApplication extends Application {
     // since getting JVM for the first time can take a long time
     // hard reference jvm from application so we are sure that it is not garbage collected
     public Jvm jvm;
+    JmxModel jmxModel;
 
     // Note: storage may be null, in this case the JmxApplication isn't persistent
     // and creates a temporary storage just like any other regular Application
@@ -100,6 +101,7 @@ public void setStateImpl(int newState) {
         if (newState != Stateful.STATE_AVAILABLE) {
             pid = UNKNOWN_PID;
             jvm = null;
+            jmxModel = null;
         }
         setState(newState);
     }

visualvm/jmx/src/org/graalvm/visualvm/jmx/impl/JmxApplicationProvider.java

@@ -385,10 +385,10 @@ public void run() {
                     } else {                        
                         app.setStateImpl(Stateful.STATE_AVAILABLE);
 
-                        model = JmxModelFactory.getJmxModelFor(app);
+                        app.jmxModel = JmxModelFactory.getJmxModelFor(app);
                         app.jvm = JvmFactory.getJVMFor(app);
 
-                        model.addPropertyChangeListener(new PropertyChangeListener() {
+                        app.jmxModel.addPropertyChangeListener(new PropertyChangeListener() {
                             public void propertyChange(PropertyChangeEvent evt) {
                                 if (evt.getNewValue() == ConnectionState.CONNECTED) {
                                     app.setStateImpl(Stateful.STATE_AVAILABLE);