RFR: 8349091: Charts: exception initializing in a background thread [v6]

[John Hendrikx]

On Tue, 25 Feb 2025 22:33:40 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

>> Root Cause:
>> (Multiple) properties are getting bound to the global `Platform.accessibilityActive` property. Binding (and I say, accessing) of properties is not thread-safe.
>> 
>> I also changed the design a bit.  Originally, every symbol in a chart had its `focusTraversableProperty` bound to `Platform.accessibilityActive` in order to enable the accessibility navigation across the chart data points.  This is rather inefficient, as the property has to manage (thousands?) of listeners.
>> 
>> Instead, a single boolean property is added to each chart, with a listener added to it which iterates over data symbols to toggle the `focusTraversableProperty` directly.
>> 
>> The exact moment when the new property gets bound is also important, and has to happen in the FX application thread.
>> 
>> With this change, it is safe to create and populate charts with data in a background thread.
>> 
>> ---
>> 
>> ## NOTES
>> 
>> 1. It looks like the `Platform.accessibilityActive` property never transitions back to false  after it transitioned to true.  Some say it is because there is no mechanism in the platform to get notified which cannot possibly be true.
>> 2. The javadoc for `Platform.accessibilityActiveProperty()` method stipulates that "_This method may be called from any thread_" which is patently not true as the current implementation is simply not thread-safe.
>> 
>> ## Note to the Reviewers
>> 
>> To avoid merge conflicts, the preferred order of integrations:
>> 
>> #1697 
>> #1713 
>> #1717
>
> Andy Goryachev has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 25 commits:
> 
>  - Merge remote-tracking branch 'origin/master' into 8349091.charts.thread.safety
>  - review comments
>  - Merge remote-tracking branch 'origin/master' into 8349091.charts.thread.safety
>  - Merge remote-tracking branch 'origin/master' into 8349091.charts.thread.safety
>  - enabled pie chart test
>  - Merge branch 'master' into 8349091.charts.thread.safety
>  - Merge branch 'master' into 8349091.charts.thread.safety
>  - whitespace
>  - Merge remote-tracking branch 'origin/master' into 8349091.charts.thread.safety
>  - cleanup
>  - ... and 15 more: https://git.openjdk.org/jfx/compare/7a7854c9...4288d1d0

modules/javafx.controls/src/main/java/javafx/scene/chart/AreaChart.java line 546:

> 544:             symbol.setAccessibleRole(AccessibleRole.TEXT);
> 545:             symbol.setAccessibleRoleDescription("Point");
> 546:             symbol.setFocusTraversable(isAccessibilityActive());

So, if I understand correctly, we can't directly do this `bind`:

    symbol.focusTraversableProperty().bind(Platform.accessibilityActiveProperty())
    
Because on a background thread there may not yet be an initialized `Platform`?  Or perhaps, `Platform` would need to initialize and we don't want to do that yet on a background thread?

-------------

PR Review Comment: https://git.openjdk.org/jfx/pull/1697#discussion_r1978188666