RFR: 8313697: [XWayland][Screencast] consequent getPixelColor calls are slow [v3]

[Alexander Zvegintsev]

On Mon, 14 Aug 2023 20:25:08 GMT, Sergey Bylokhov <serb at openjdk.org> wrote:

>> Alexander Zvegintsev has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   fix app exit issue
>
> src/java.desktop/unix/classes/sun/awt/screencast/ScreencastHelper.java line 127:
> 
>> 125:             @Override
>> 126:             public void run() {
>> 127:                 closeSession();
> 
> What happen if the "closeSession" is executed why the new Robot#getRGBPixels is called? In the robot code we call timerCloseSessionRestart to restart/cancel timer, but I think it could be possible that closeSession() is already executed and may close session right before it will be used by the robot but after we "open" it. 
> 
> Or this case is not possible?

Both `ScreencastHelper#getRGBPixels`(`Robot#getRGBPixels` calls it internally) and `ScreencastHelper#closeSession` are synchronized. 
So `ScreencastHelper#closeSession` will wait until the execution of `ScreencastHelper#getRGBPixels` is finished and vice versa.

Many hours of testing with random delays close to DELAY_BEFORE_SESSION_CLOSE worked fine.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15250#discussion_r1294037138