Platform.runLater() sometimes too slow ( invoked after 4-5 seconds)

Question

Normally the JavaFX-UI gets updated within a resonable time (e.g. <0.1 sec) however sometimes this update takes 4-5 seconds, from the ressource monitor I cannot see any suspicious CPU or MEM consumption. I know that there is no other way to update the UI (as discussed here: Re: Correct way of async updates?
Is there a way to track or monitor the state of the event queue ? Where is it hanging ?

Answer 1

I am using JavaVisualVM, the "Heap size" grows whenever I create a new Scene and put is to the Stage (stage.setScene(..)), the "Used Heap" is growing as well a little. Once the "Heap size" has reached the 90MB value my GUI is freezing. Just in that very moment. ?
Why won't the GarbageCollector free the memory of the non used Scenes ?
I made a small app to show this issue, by clicking the Button ("Make new") 3 or 4 times an Excpetion will be thrown. (by Running the code below with small heap: -Xms10m -Xmx16m )
Why is this ? The former scene is not referenced anymore ? Why does the heap keep growing until the Exception ?
import java.util.Random;
import javafx.application.Application;
import javafx.application.Platform;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
public class TestFX extends Application {
     Stage pStage;
     Random randomGenerator = new Random();
     @Override
     public void start(Stage stage) throws Exception {          
          pStage = stage;
          Platform.runLater(new Runnable() {
                 public void run() {
                    StackPane stack = new StackPane();
                    stack.setPrefWidth( 640);
                    stack.setPrefHeight( 480);
                    stack.setAlignment( Pos.TOP_LEFT);
                    for (int i=0; i<100;i++){
                         Button but = new Button("Button " + i);
                         int randomX = randomGenerator.nextInt( 620);
                         int randomY = randomGenerator.nextInt( 470);
                         but.setTranslateX( randomX);
                         but.setTranslateY( randomY);
                         stack.getChildren().add( but);
                    Button makeNewButton = new Button("Make new");
                    makeNewButton.setStyle("-fx-font: 22 arial; -fx-base: #b6e7c9;");
                    makeNewButton.setOnAction( new EventHandler<ActionEvent>() {
                         @Override
                         public void handle(ActionEvent arg0) {     
                              try {
                                   start( pStage);
                              } catch (Exception e) {
                                   // TODO Auto-generated catch block
                                   e.printStackTrace();
                    BorderPane border = new BorderPane();
                    border.setTop( makeNewButton);
                    border.setCenter( stack);
                    Scene scene = new Scene( border, 640, 480, Color.WHITESMOKE);
                    pStage.setScene( scene);
                    pStage.show();
     public static void main(String[] args) throws Exception{          
        Application.launch(args);
Edited by: Marcello on 26.06.2012 08:10