Concurrency in JavaFX - task is not finished - multithreading

Question

I have two tasks, one to change screen opacity, the other to perform a complex computation. I wanted the computation to begin only after the screen fading has actually changed so I wrote the following:
Task<Void> task = new Task<Void>() {
#Override
protected Void call() throws Exception {
stage.getScene().getRoot().setOpacity(0.2);
stage.show();
return null;
}
};
Task<Void> task2 = new Task<Void>() {
#Override
protected Void call() throws Exception {
// Complex computation
return null;
}
};
task.setOnSucceeded(new EventHandler<WorkerStateEvent>() {
#Override
public void handle(WorkerStateEvent paramT) {
// this busy waiting line was added in attempt to force the
// fading before beginning second task
while (stage.getScene().getRoot().getOpacity() != 0.2) {}
stage.show();
Platform.runLater(task2);
}
});
task2.setOnSucceeded(new EventHandler<WorkerStateEvent>() {
#Override
public void handle(WorkerStateEvent paramT) {
stage.getScene().getRoot().setOpacity(1);
stage.show();
}
});
task.run();
However, sometimes I see the computation beginning and the screen fading only after it's done. Sometimes it does work. So I think there's a threading issue here. Note: When I'm on debug mode and stop at each task it really works everytime. What can be done to force the screen fade before the second task begins?
EDIT:
As suggested, I changed the code to the following:
Task<Void> task1 = new Task<Void>() {
#Override
protected Void call() throws Exception {
// Long computation
return null;
}
};
Task<Void> task = new Task<Void>() {
#Override
protected Void call() throws Exception {
FadeTransition ft = new FadeTransition(Duration.millis(1), stage.getScene().getRoot());
ft.setFromValue(1.0);
ft.setToValue(0.1);
ft.setCycleCount(1);
//ft.setAutoReverse(true);
ft.play();
ft.setOnFinished(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent event) {
new Thread(task1).run();
}
});
return null;
}
};
task1.setOnSucceeded(new EventHandler<WorkerStateEvent>() {
#Override
public void handle(WorkerStateEvent paramT) {
FadeTransition ft1 = new FadeTransition(new Duration(0.1), stage.getScene().getRoot());
ft1.setFromValue(0.1);
ft1.setToValue(1.0);
ft1.setCycleCount(1);
//ft.setAutoReverse(true);
ft1.play();
//stage.show();
}
});
new Thread(task).run();
Still I see the same behavior.

Answer 1

Replace
new Thread(task).run();
with
new Thread(task).start();