RFR: 8221261: deadlock of CInputMethod.characterIndexForPoint and webkit.InputMethodClientImpl.getLocationOffset

[Kevin Rushforth]

On Fri, 22 Dec 2023 11:27:00 GMT, Johannes Bechberger <jbechberger at openjdk.org> wrote:

> A dead-lock is caused by the interaction of MacOS, the AWTEventQueue and JavaFX when the users pressed the Caps Lock key while the AWTEventQueue is processing another event (more on this in the issue). The bug depends on the specific timing of the event sending and can apparently be prevented by finishing all incoming OS events directly while the LWCToolkit.invokeAndWait method is executed.
> 
> This fix is tested and fixes the issue.
> 
> I attached a small
> [reproducer](https://github.com/openjdk/jdk/files/13751865/Archive.zip), just run it with `mvn install package javafx:run`.

I note that your proposed solution was originally pointed out as a workaround by Arunprasad Rajkumar in [this JBS comment](https://bugs.openjdk.org/browse/JDK-8221261?focusedId=14255770&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14255770).

One possible problem with the above workaround is mentioned in [this comment](https://github.com/openjdk/jdk/blob/bef94378ddf33ab29a36e1ceee48890a5b5c7a9d/src/java.desktop/macosx/classes/sun/lwawt/macosx/LWCToolkit.java#L930) describing the `processEvents` parameter (the one you are changing from `false` to `true`) in the `doAWTRunLoop` method:

"Additional attention is needed when using this feature as we short-circuit normal event processing which could break Appkit"

Anton Tarasov proposed a modified solution, in [this JBS comment](https://bugs.openjdk.org/browse/JDK-8221261?focusedId=14263545&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14263545), that spins up a nested event loop that processes events only for the `firstRectForCharacterRange` and `characterIndexForPoint` methods in `CInputMethod`. Presuming that this is the right place to fix it, this seems a safer approach, although still needs to be evaluated.

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PR Comment: https://git.openjdk.org/jdk/pull/17184#issuecomment-1867861682