copy / paste the following piece of code and try running. Once you have started a gui less JavaFX thread you can not stop it anymore, not even if you use Thread.currentThread().getThreadGroup().interrupt();



import java.lang.management.ManagementFactory;
import java.lang.management.ThreadMXBean;
import javafx.application.Platform;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.concurrent.Worker;
import javafx.embed.swing.JFXPanel;
import javafx.scene.web.WebEngine;
import javafx.scene.web.WebView;
import netscape.javascript.JSObject;

public class D31 extends Thread {
    private static JFXPanel USELESS = new JFXPanel();
    
    public static synchronized void main(String[] args) throws InterruptedException {
        System.out.println("begin of main " + Thread.currentThread());
        D31 d31 = new D31();
        
        Platform.runLater(d31);
        // d31.wait();
        
        System.out.println("end of main " + d31);
    }
    
    public synchronized void run() {
        final Thread THIS = this;
        final WebView webView = new WebView();
        final WebEngine engine = webView.getEngine();
        System.out.println("begin run " + Thread.currentThread() );
        
        //final WebEngine engine = new WebEngine();
        //engine.documentProperty().addListener( new ChangeListener<Document>() { @Override public void changed(ObservableValue<? extends Document> prop, Document oldDoc, Document newDoc) {
        engine.getLoadWorker().stateProperty().addListener(new MyListner(engine));
    
       
        engine.load("http://google.com");
        // try { this.wait(); } catch (Exception e) { e.printStackTrace(); }
        System.out.println("end of start");
        
        // try { this.stop(); } catch (Exception e) {}
    }
    
    /*
    public void exit() {
       Platform.runLater( new Runnable(){@Override public void run(){
          System.out.println( "exit/runLater/run" );
          engine.getLoadWorker().cancel();
          Platform.exit();
       }});
    }*/
   
    public ThreadGroup getRootThreadGroup( ) {
        
        ThreadGroup tg = Thread.currentThread( ).getThreadGroup( );
        ThreadGroup ptg;
        while ( (ptg = tg.getParent( )) != null )
            tg = ptg;
        return tg;
    }

    public ThreadGroup[] getAllThreadGroups( ) {
        final ThreadGroup root = getRootThreadGroup( );
        int nAlloc = root.activeGroupCount( );
        int n = 0;
        ThreadGroup[] groups;
        do {
            nAlloc *= 2;
            groups = new ThreadGroup[ nAlloc ];
            n = root.enumerate( groups, true );
        } while ( n == nAlloc );

        ThreadGroup[] allGroups = new ThreadGroup[n+1];
        allGroups[0] = root;
        System.arraycopy( groups, 0, allGroups, 1, n );
        
        for (ThreadGroup tg : allGroups) {
            System.out.println("group: " + tg);
            for (Thread t : getGroupThreads(tg)) {
                System.out.println("\t: " + t);
            }
        }
        
        return allGroups;
    }
    
    Thread[] getGroupThreads( final ThreadGroup group ) {
        if ( group == null )
            throw new NullPointerException( "Null thread group" );
        int nAlloc = group.activeCount( );
        int n = 0;
        Thread[] threads;
        do {
            nAlloc *= 2;
            threads = new Thread[ nAlloc ];
            n = group.enumerate( threads );
        } while ( n == nAlloc );
        return java.util.Arrays.copyOf( threads, n );
    }
    
    Thread[] getAllThreads( ) {
        final ThreadGroup root = getRootThreadGroup( );
        final ThreadMXBean thbean = ManagementFactory.getThreadMXBean( );
        int nAlloc = thbean.getThreadCount( );
        int n = 0;
        Thread[] threads;
        do {
            nAlloc *= 2;
            threads = new Thread[ nAlloc ];
            n = root.enumerate( threads, true );
        } while ( n == nAlloc );
        return java.util.Arrays.copyOf( threads, n );
    }

    public void log(String msg) {
        System.out.println(msg);
    }
    
    public class MyListner implements ChangeListener<Worker.State> {
            private final WebEngine engine;
            
            public MyListner(WebEngine engine) {
                this.engine = engine;
            }
            
            public void changed(ObservableValue ov, Worker.State oldState, Worker.State newState) {
                System.out.println("changed " + Thread.currentThread() + " " + newState + " " + ov);
                
                if (newState == Worker.State.SUCCEEDED) {
                    JSObject jsobj = (JSObject) engine.executeScript("window");
                    jsobj.setMember("console", this);
        
                    //System.out.println(DomUtils.getDocumentString(engine.getDocument()));
                    System.out.println(engine.getDocument());
                    
                    Platform.setImplicitExit(true);
                    // engine.executeScript("println('-----------------------lala');");
                    // try { Thread.sleep(1000); } catch (Exception e) {}
                    
                    System.out.println("want exit " + Thread.currentThread() );
                    // getAllThreadGroups();
                    
                    Platform.setImplicitExit(false);
                    engine.getLoadWorker().cancel();
                    Platform.exit();
                    
                    Thread.currentThread().getThreadGroup().interrupt();
                    for (Thread t : getAllThreads()) {
                        System.out.println(t.getName());
                        //if (t.getName().contains("URL")||t.getName().contains("FX")||t.getName().contains("Quant")) {
                        if (!t.getName().contains("Thread")) {
                            t.interrupt();
                            System.out.println(t.getState());
                        }
                    }
                    try { Thread.sleep(1000); } catch (Exception e) {}
                    
                    // getAllThreadGroups();
                  
                    
                    // System.out.println(THIS.isAlive());
                    // engine.getLoadWorker().cancel();
                    Platform.exit(); // platform will not exit ...
                    // exit();
                }
            
                /*
                USELESS.invalidate();
                USELESS = null;
                System.out.println(engine.getLoadWorker().cancel());
                Platform.exit();
                
                engine.getLoadWorker().stateProperty().removeListener(this);
                */
            }
        }
}