RFR: 4200096: OffScreenImageSource.removeConsumer NullPointerException [v4]

[Jeremy]

On Wed, 12 Apr 2023 08:09:42 GMT, Jeremy <duke at openjdk.org> wrote:

>> This resolves a 25 year old P4 ticket: a NullPointerException is printed to System.err needlessly.
>> 
>> This resolution involves confirming that an ImageConsumer is still registered before every notification.
>> 
>> I'll understand if this is rejected as unimportant, but I stumbled across this in the real world the other day and thought this was a simple enough bug to practice on.
>
> Jeremy has updated the pull request incrementally with one additional commit since the last revision:
> 
>   4200096: rewrite solution, only print stacktrace if theConsumer != null
>   
>   I don't like that we're *expecting* a NullPointerException to get thrown in the course of an allowed use case, but that's probably just a preferences on my part. More importantly: this branch passes all new unit tests. Plus it's readable and easy to code review.
>   
>   This is related to the latest round of PR feedback here:
>   https://github.com/openjdk/jdk/pull/13408#issuecomment-1504605358

I just pushed an update that uses the null-check for `theConsumer`, but it otherwise still expects the NPE.

Regarding the System property / debugger message:

If we established that removing the listener before production is complete is an OK thing to do, then do you still want this debugger output? (Or to put that another way: do you think that will really get used?) I don't have a lot of experience with debugger output from sun classes, so if you think it's helpful I'll take your word for it.

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PR Comment: https://git.openjdk.org/jdk/pull/13408#issuecomment-1504854806