RFR: 8357067: Platform preference change can emit multiple notifications [v2]

[Andy Goryachev]

On Thu, 15 May 2025 18:56:14 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

>> Some platform preference changes can trigger the emission of multiple notifications. For example, when switching from a high-contrast theme on Windows to the regular theme, the following notifications are emitted (log can be viewed in `PlatformPreferencesChangedTest`):
>> 
>> 
>> changed:
>> 	Windows.UIColor.Accent=0x0078d4ff
>> 	Windows.SysColor.COLOR_HIGHLIGHTTEXT=0xffffffff
>> 	Windows.SysColor.COLOR_WINDOW=0xffffffff
>> 	Windows.UIColor.AccentLight1=0x0091f8ff
>> 	Windows.SysColor.COLOR_3DFACE=0xf0f0f0ff
>> 	Windows.SysColor.COLOR_HOTLIGHT=0x0066ccff
>> 	Windows.SysColor.COLOR_WINDOWTEXT=0x000000ff
>> 	Windows.SysColor.COLOR_BTNTEXT=0x000000ff
>> 	Windows.UIColor.Foreground=0x000000ff
>> 	Windows.UIColor.AccentDark1=0x0067c0ff
>> 	Windows.UIColor.Background=0xffffffff
>> 	Windows.UIColor.AccentLight3=0x99ebffff
>> 	Windows.UIColor.AccentLight2=0x4cc2ffff
>> 	Windows.SysColor.COLOR_GRAYTEXT=0x6d6d6dff
>> 	Windows.SysColor.COLOR_HIGHLIGHT=0x0078d7ff
>> 	Windows.UIColor.AccentDark2=0x003e92ff
>> 	Windows.UIColor.AccentDark3=0x001a68ff
>> 
>> changed:
>> 	-Windows.SPI.HighContrastColorScheme
>> 	Windows.SPI.HighContrast=false
>> 
>> changed:
>> 	Windows.UIColor.Foreground=0xffffffff
>> 	Windows.UIColor.Background=0x000000ff
>> 
>> 
>> Notably, the values for Windows.UIColor.Foreground/Background are inconsistent between the notifications (although they are eventually correct). In general, only a single notification should be emitted that includes all of the changed preferences.
>> 
>> This artifact is only visible on Windows. The reason is that changing some system settings (like high-contrast theme) causes a number of different window messages to be sent to the application. We should wait for all window messages to come in, and then aggregate all of the changed preferences into a single notification.
>> 
>> In order to minimize the delay between changing a system setting and sending out the notification in JavaFX, the implementation only waits when instructed to do so by the native toolkit. This allows us to instantly send out notifications for most changes, but selectively wait a bit for changes where the native toolkit knows that more changes might be coming in.
>
> Michael Strauß has updated the pull request incrementally with one additional commit since the last revision:
> 
>   simplified DelayedChangedAggregator

I am not comfortable with this change, as it falls under application requirements.

The function of the JavaFX platform is to communicate the OS events as faithfully as it can, in my opinion.  If the application requirements call for some debouncing, especially that with a one second delay, then the application is free to implement that.

If, however, the application requirements call for no delay, this change makes it impossible.

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

PR Comment: https://git.openjdk.org/jfx/pull/1810#issuecomment-2884795670