Javafx application is still running in background even after closing - javafx

Question

I'm having a problem closing my JavaFX application. The application keeps running in the background even after closing. I think the actual problem is caused due to the alert box which will popup while closing the application for confirmation, if the alert doesn't pop up (on certain conditions) then the application exits normally.
Actually, I want the user to confirm whether to save the file or not before closing the application so I have added an alert box that will show only if the file is not saved manually (using Ctrl+S or File->Save option) before closing the application. When the popup appears, if the user selects to save the file it will save as usual if it chooses to cancel then the application continues to run.
But the problem is that if the alert box appears for confirmation and the user chooses to save or don't save option then the application doesn't close completely (even after completing all the task related to saving if the user chooses to save the file) it only hides the stage and keeps running in the background but if the alert box doesn't appear for confirmation then the application closes normally.
Here is the code for widow.setOnCloseRequest(); event:-
Platform.runLater(() -> {
window = App.getStage();
window.setOnCloseRequest(event -> {
if (!saveIfFileEdited()) {
event.consume();
} else {
scheduledService.shutdown();
// Platform.exit(); //I have tried this also but it dosen't work.
}
});
});
Here it will call the saveIfFileEdited() method which will handle the alert popup for confirmation & and here is its code:-
private boolean saveIfFileEdited() {
if (isEdited.get()) { // this will check if the file was edited but not saved.
Alert fileEditedAlert = new Alert(Alert.AlertType.CONFIRMATION);
fileEditedAlert.setTitle("Notepad");
fileEditedAlert.setHeaderText(null);
fileEditedAlert.setContentText("Do you want to save the changes to " + windowTitle.get() + "?");
ButtonType save = new ButtonType("Save");
ButtonType dontSave = new ButtonType("Don't Save");
fileEditedAlert.getButtonTypes().setAll(save, dontSave, ButtonType.CANCEL);
Optional<ButtonType> result = fileEditedAlert.showAndWait();
if (result.isPresent() && result.get().equals(save)) {
handleSaveFile(null); // this func will save the file, it may open save file dialog if the file is going to be saved for first time.
return true;
} else if (result.isPresent() && result.get().equals(dontSave)) {
return true;
} else if (result.isPresent() && result.get().equals(ButtonType.CANCEL)) {
return false;
} else {
return false;
}
} else {
return true;
}
}
Please help me to resolve this issue.
I cannot close the JVM forcefully using System.exit(0); because there may be some task in another thread which has to be completed even after closing the application.
Thanks.