HEADS-UP: Threading restriction for Animation play, pause, stop now enforced USE CASE

Wed Jan 24 13:29:39 UTC 2024

Hi Kevin

If I may make one more final appeal then to an alternative solution please.

Could we then instead of throwing an Exception rather invoke runLater if  
needed inside play, stop, and resume.

Putting the onus on the developer is fine if it is the developer that is  
invoking the call, but if it's in a library then it's a no go.

In my application I have two libraries that I know of where this happens.  
The major problem is that with FX22 as it now stands my application just  
crashes because play() does an FX thread check and throws an Exception  
which it never did before. There are bound to be other applications out  
there that are going to find themselves in a similar position.

PLEASE !

Regards
Jurgen

On Wed, 24 Jan 2024 15:15:31 +0200, Kevin Rushforth  
<kevin.rushforth at oracle.com> wrote:

> Thank you to Jurgen for raising the question and to Nir, John, and  
> Michael for evaluating it.
>
> I conclude that there is insufficient motivation to revert the change in  
> behavior implemented by JDK-8159048 to allow calling the  
> play/>pause/stop methods of Animation on a background thread. Doing so  
> without making it fully multi-thread-safe would be asking for problems,  
> >and making it fully multi-thread-safe would be a fair bit of work to do  
> it right without a clear benefit.
>
> We will proceed with the current approach and let JDK-8159048 stand.  
> Further, we will proceed with  
> https://bugs.openjdk.org/browse/>JDK-8324219 which is under review in  
> https://github.com/openjdk/jfx/pull/1342
>
> -- Kevin
>
> On 1/24/2024 12:30 AM, Nir Lisker wrote:
>> After playing around with the code sample, I think that this is not the  
>> right way to use the animation. The reason is that there is >>no point  
>> in starting the animation before the control is attached to the  
>> scenegraph, or even made visible. A small refactoring >>where, e.g.,  
>> the controller class exposes a method to start the animation in  
>> onSucceeded or just calls it on the FX thread is >>enough. I never  
>> start an animation as part of the construction because it's not the  
>> right time. John suggested tying the lifecycle >>of the animation to  
>> the showing of the node, which also solves the problem.  
>> There are animations like PauseTransition or other non-interfering  
>> Timelines that could reasonably be run on a background >>thread. Or  
>> maybe just on an unconnected control. This could be a reason to not  
>> limit animation methods to the FX thread at >>the expense of possible  
>> user errors, but document the pitfall.
>>
>> I don't see a good use case for modifying controls in a background  
>> thread while still interacting with the scenegraph, hence for >>adding  
>> multithread support.
>> - Nir
>>
>> On Mon, Jan 22, 2024, 12:59 Jurgen Doll <javafx at ivoryemr.co.za> wrote:
>>> Here's an example as requested by Nir:
>>>
>>>>>> public class FxTimeLineTest extends Application
>>>
>>> {
>>>
>>>    private BorderPane bp = new BorderPane( new Label("Loading") );
>>>
>>>
>>>
>>>    public static void main( String[] args ) {
>>>
>>>        launch( FxTimeLineTest.class, args );
>>>
>>>    }
>>>
>>>
>>>
>>>    @Override
>>>
>>>    public void start( Stage primaryStage ) throws Exception {
>>>
>>>        new Thread( new LoadScene() ).start();
>>>
>>>        primaryStage.setScene(new Scene( bp, 300, 200 ) );
>>>
>>>        primaryStage.setTitle( "Memory Usage" );
>>>
>>>        primaryStage.show();
>>>
>>>    }
>>>
>>>
>>>
>>>    private class LoadScene extends Task<Parent> {
>>>
>>>        @Override protected Parent call() throws Exception {
>>>
>>>            Parent p = FXMLLoader.load( getClass(
>>> ).getResource("TestView.fxml") );
>>>
>>>            Thread.sleep( 1000 );
>>>
>>>            return p;
>>>
>>>        }
>>>
>>>
>>>
>>>        @Override protected void succeeded() {
>>>
>>>            bp.setCenter( getValue() );
>>>
>>>        }
>>>
>>>
>>>
>>>        @Override protected void failed() {
>>>
>>>            getException().printStackTrace();
>>>
>>>        }
>>>
>>>    }
>>>
>>> }
>>>
>>>
>>> ------------------------------------------------------------------------------------------------------
>>>
>>>
>>> public class TestView
>>>
>>> {
>>>
>>>    @FXML private Label memory;
>>>
>>>
>>>
>>>    private static final double  MEGABYTE = 1024 * 1024;
>>>
>>>
>>>
>>>    @FXML private void initialize()
>>>
>>>    {
>>>
>>>        var updater = new Timeline
>>>
>>>        (
>>>
>>>            new K
>>> eyFrame( Duration.seconds(2.5), event ->
>>>
>>>            {
>>>
>>>                var runtime = Runtime.getRuntime();
>>>
>>>                double maxMemory = runtime.maxMemory() / MEGABYTE;
>>>
>>>                double usedMemory = (runtime.totalMemory() -  
>>> runtime.freeMemory()) / MEGABYTE;
>>>
>>>                memory.setText( (int) usedMemory + " MB / " + (int)  
>>> maxMemory +" MB" );
>>>
>>>            })
>>>
>>>        );
>>>
>>>
>>>
>>>        updater.setCycleCount(Animation.INDEFINITE);
>>>        // This FXML is being loaded on a background thread
>>>
>>>        updater.play();
>>>
>>>    }
>>>
>>> }
>>>
>>>
>>> ------------------------------------------------------------------------------------------------------
>>>
>>> TestView.fxml
>>>
>>> <?xml version="1.0" encoding="UTF-8"?>
>>>
>>>
>>>
>>> <?import javafx.scene.control.Label?>
>>>
>>> <?import javafx.scene.layout.StackPane?>
>>>
>>>
>>>
>>> <StackPane xmlns:fx="http://javafx.com/fxml/1"  
>>> fx:controller="TestView">
>>>
>>>   <children>
>>>
>>>      <Label fx:id="memory" text="Current / Max MB" >
>>>
>>>         <properties hashCode="12345" />
>>>
>>>      </Label>
>>>
>>>   </children>
>>>
>>> </StackPane>
>>>
>>>
>>>
>>> On Sat, 20 Jan 2024 17:08:41 +0200, Nir Lisker <nlisker at gmail.com>  
>>> wrote:
>>>
>>>> Hi Jurgen,
>>>> What I'm confused about the most is what it is you are actually  
>>>> trying to do that necessitates the use of animations outside >>>>of  
>>>> the FX thread. You said that you need to initialize controls on  
>>>> another thread, and that you are using Task (both of which >>>>are  
>>>> fine), but how does playing animations relate? Playing an animation  
>>>> is something that is done explicitly, usually in >>>>order to  
>>>> manipulate data. Can you give a real use case, like a minimized  
>>>> version of what you're doing?
>>>>
>>>> - Nir
>

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