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

[Alexander Zvegintsev]

On Fri, 11 Aug 2023 17:19:40 GMT, Alexander Zvegintsev <azvegint at openjdk.org> wrote:

> Right now, each call to getPixelColor/createScreenCapture opens and closes a ScreenCast session. 
> When there are many such calls in a row, it becomes a rather time-consuming operation.
> 
> For example,
> 
> 
> for (int i = 0; i < 50; i++) {
>     for (int j = 0; j < 50; j++) {
>         robot.getPixelColor(i, j);
>     }
> } 
> 
> `50x50 took 375219ms`
> 
> This fix offers optimization by keeping the session open and closing it only 2 seconds after the last activity.
> 
> `50x50 took 28113ms` which is ~ 13 times faster.
> 
> Testing looks good.

src/java.desktop/unix/native/libawt_xawt/awt/screencast_pipewire.c line 96:

> 94:             if (screenProps->data->stream) {
> 95:                 fp_pw_stream_disconnect(screenProps->data->stream);
> 96:                 fp_pw_thread_loop_lock(pw.loop);

Moving `pw_stream_disconnect` call out of this lock fixes [JDK-8310334](https://bugs.openjdk.org/browse/JDK-8310334)

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PR Review Comment: https://git.openjdk.org/jdk/pull/15250#discussion_r1291611941