JavaFX in Default Window Error on Quit

[vsquared]

The following code demonstrates a round button in the default Processing window but the button's 'quit' action throws an exception when using exit_sketch(). The issue seems to be due to shutting down a Processing window which is running a JavaFX Application Thread. Exception thrown is Not on FX application thread; currentThread = JavaFX Application Thread

# Uses Imported mode for py5

# Error on 'quit': Not on FX application thread; currentThread = JavaFX Application Thread

import javafx

_wndW = 400
_wndH = 400

def myBtnAction(event):
# Works, but throws exception
  exit_sketch()

def settings():
  size(_wndW,_wndH,FX2D)
  
def setup():
  canvas = get_surface().get_native()
  window_title('JavaFX Round Button in Default Window')
  canvas = get_surface().get_native()
  root = canvas.getParent()
  pane = javafx.scene.layout.Pane()
  root.getChildren().add(pane)
  quitBtn = javafx.scene.control.Button("Q")
  quitBtn.setStyle("-fx-background-radius:5em;"+"-fx-min-width:30px;"+"-fx-min-height:30px;"+"-fx-max-width:30px;"+"-fx-max-height:30px;")
  quitBtn.setLayoutX(_wndW - 50)
  quitBtn.setLayoutY(20)
  quitBtn.setOnAction(myBtnAction)
  pane.getChildren().add(quitBtn)
  

Output:

Addendum:
Just found out it works as expected on Linux. May only be a problem on Mac. JavaFX currently not working on Windows (known problem).

[hx2A]

Just found out it works as expected on Linux. May only be a problem on Mac. JavaFX currently not working on Windows (known problem).

Can you try moving the exit_sketch() call to in thedraw() function? Something like:

exit_flag = False

def myBtnAction(event):
    global exit_flag
    exit_flag = True

...

def draw():
    if exit_flag:
        exit_sketch()

MacOS is very particular about the main thread and will only allow that thread to perform certain actions.

[vsquared]

Error message is the same with this technique; code follows if you want to try it for yourself:

# Uses Imported mode for py5
# Error on 'quit': Not on FX application thread; currentThread = JavaFX Application Thread

import javafx

_wndW = 400
_wndH = 200

exit_flag = False

def myBtnAction(event):
  global exit_flag  
  exit_flag = True
  
def setup():
  size(_wndW,_wndH,FX2D)
  canvas = get_surface().get_native()
  window_title('JavaFX Round Button in Default Window')
  canvas = get_surface().get_native()
  root = canvas.getParent()
  pane = javafx.scene.layout.Pane()
  root.getChildren().add(pane)
  quitBtn = javafx.scene.control.Button("Q")
  quitBtn.setStyle("-fx-background-radius:5em;"+"-fx-min-width:30px;"+"-fx-min-height:30px;"+"-fx-max-width:30px;"+"-fx-max-height:30px;")
  quitBtn.setLayoutX(_wndW - 50)
  quitBtn.setLayoutY(20)
  quitBtn.setOnAction(myBtnAction)
  pane.getChildren().add(quitBtn)

def draw():
  if exit_flag:
    exit_sketch()
    print("exit called.")

Error Message:

java.lang.IllegalStateException: Not on FX application thread; currentThread = JavaFX Application Thread
	at javafx.graphics/com.sun.javafx.tk.Toolkit.checkFxUserThread(Toolkit.java:295)
	at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.checkFxUserThread(QuantumToolkit.java:458)
	at javafx.graphics/javafx.stage.Window.setShowing(Window.java:1189)
	at javafx.graphics/javafx.stage.Window.hide(Window.java:1215)
	at javafx.graphics/com.sun.javafx.stage.WindowPeerListener.closed(WindowPeerListener.java:105)
	at javafx.graphics/com.sun.javafx.tk.quantum.GlassWindowEventHandler.run(GlassWindowEventHandler.java:144)
	at javafx.graphics/com.sun.javafx.tk.quantum.GlassWindowEventHandler.run(GlassWindowEventHandler.java:40)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:400)
	at javafx.graphics/com.sun.javafx.tk.quantum.GlassWindowEventHandler.lambda$handleWindowEvent$4(GlassWindowEventHandler.java:178)
	at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:424)
	at javafx.graphics/com.sun.javafx.tk.quantum.GlassWindowEventHandler.handleWindowEvent(GlassWindowEventHandler.java:176)
	at javafx.graphics/com.sun.glass.ui.Window.handleWindowEvent(Window.java:1336)
	at javafx.graphics/com.sun.glass.ui.Window.notifyDestroy(Window.java:1250)
2025-06-18 00:01:58.392 Python[4562:220992] WARNING: Secure coding is not enabled for restorable state! Enable secure coding by implementing NSApplicationDelegate.applicationSupportsSecureRestorableState: and returning YES.

[vsquared]

The solution is to get the stage from the default window and then use stage.close().

# Uses Imported mode for py5

import javafx

_wndW = 400
_wndH = 200

def myBtnAction(event):
  global stage
  stage.close()
  
def setup():
  global stage
  
  size(_wndW,_wndH,FX2D)
  get_surface().set_always_on_top(True)
  window_title('JavaFX Round Button in Default Window')
  canvas = get_surface().get_native()
  root = canvas.getParent()
  scene = root.getScene()
  stage = scene.getWindow()
  pane = javafx.scene.layout.Pane()
  root.getChildren().add(pane)
  quitBtn = javafx.scene.control.Button("Q")
  quitBtn.setStyle("-fx-background-radius:5em;"+"-fx-min-width:30px;"+"-fx-min-height:30px;"+"-fx-max-width:30px;"+"-fx-max-height:30px;")
  quitBtn.setLayoutX(_wndW - 50)
  quitBtn.setLayoutY(20)
  quitBtn.setOnAction(myBtnAction)
  pane.getChildren().add(quitBtn)

[hx2A]

I just tested the following code on Linux, MacOS, and Windows, and it worked on all of them.

def setup():
    py5.size(400, 400, py5.FX2D)

def draw():
    py5.rect(py5.mouse_x, py5.mouse_y, 10, 10)

def key_pressed():
    py5.exit_sketch()

The exit_sketch() method does work in this case because it is being called from one of py5's own event functions. In your example, it is being called from a button you made in JavaFX and the event is being triggered outside of py5.

Interesting that this matters. In any case, your solution is the right one for what you want to do.

[hx2A]

I just tested the following code on Linux, MacOS, and Windows, and it worked on all of them.

Ooops, I must have been confused. I get the same IllegalStateException on MacOS. I have an idea for how to fix this.

[vsquared]

The FX2D window is a JavaFX window, so you have to stop the JavaFX Application Thread as far as I can tell.