Thought experiment: constructing Nodes on a different thread...

[John Hendrikx]

Thanks, it seems I misunderstood something fundamental here.

I always figured the memory effects are limited to the variables 
accessed/mutated within a synchronized block (or *could* be limited to 
just those by selectively flushing data by some advanced VM).  
Apparently that's not the case, and a full flush is simply done after a 
synchronized block completes, which would include all mutated fields, 
not just those inside a synchronized block.

--John

On 25/01/2024 15:50, Kevin Rushforth wrote:
> Yes, I think you are missing something. Unless you have an animation 
> that just decides all on it's own to find and attach a newly 
> discovered node to the scene and start rendering it, there will be a 
> synchronization as a result of calling runLater. Consider the 
> following code:
>
>     Label label = new Label();
>     label.setText("hi");
>
>     // Attach it to the scene on the FX thread.
>     Platform.runLater(()  -> root.getChildren().add(label));
>
> The "runLater" necessarily synchronizes with the FX Application thread 
> so that the runnable can be put on its queue and later taken off the 
> queue and executed on the FX Application thread. As specified in the 
> Platform::runLater API docs: Actions in a thread prior to submitting a 
> runnable to this method happen-before actions performed by the 
> runnable in the JavaFX Application Thread.
>
> So I don't see the problem.
>
> -- Kevin
>
>
> On 1/25/2024 1:50 AM, John Hendrikx wrote:
>> All this threading talk has made me wonder something:
>>
>> Let's say there are two threads, the FX thread and Thread 1.  I do 
>> the following:
>>
>> - On thread 1: create Label
>> - On thread 1: set Label text to "xyz"
>>
>> I now attach this label to an active Scene graph. This should be done 
>> on the FX thread as we're going to be manipulating an active Scene 
>> graph, so:
>>
>> - On FX thread: attach Label to active scene graph
>>
>> There is no synchronization in place on the Label's text field. What 
>> guarantees do I have that when the label is shown on screen it will 
>> show "xyz" ?
>>
>> IMHO, there is no such guarantee, and so any creation or manipulation 
>> of Nodes that will later be part of an active scene graph (and thus 
>> accessed by the FX thread) **must** be done on the FX thread.  
>> Involving any other thread in their creation or manipulation runs the 
>> risk of seeing an object in the incorrect state (or even an 
>> "impossible" state when multiple fields are involved that normally 
>> change together).
>>
>> Effectively, assuming that when you create Nodes you always have the 
>> intention of showing them at some point, you can never construct 
>> Nodes on any other thread than the FX thread...
>>
>> Am I missing something?
>>
>> --John
>>
>