[JENKINS-72796] stable context classloader for Computer.threadPoolForRemoting

[jtnord]

Whilst the threadpool used reset the context classloader at the end of any task, it did not ensure that the initial classloader used was anything sepcific, rather it would use whatever the calling threads contextClassLoader was.

This is now fixed as we use the Jenkins WebApp classloader (same as the Timer) which is used by (A)PeriodicTasks.

Whilst we should really not have a context classloader (aka null) and this should be set where needed by code, almost everywhere in Jenkins the context classloader is already the webapp classloader, and so setting this to be different depending on how things where called would seemingly be a little scary. Arguably this and other context classloaders should be all set to null and any code that wants different should be changed, but this is a larger piece of work that would have potential impact on an unknown number of plugins in the ecosystem, so this fix uses what was set > 90% of the time.

See JENKINS-72796.

Testing done

Proposed changelog entries

• Ensure threads in the Computer.threadPoolForRemotingexecutor service always have the Jenkins webapp ClassLoader set as the context ClassLoader to prevent random class loading issues when code is running in this ExecutorService.

Proposed upgrade guidelines

N/A

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@mention

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[timja]

/label ready-for-merge

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This PR is now ready for merge, after ~24 hours, we will merge it if there's no negative feedback.

Thanks!

[kmartens27]

Hi @jtnord, would there be a better version of the changelog entry for this PR? If there should not be a changelog entry, we can definitely adjust, but if there should be something included, would you be able to clarify a bit what that would be?

[jtnord]

Hi @jtnord, would there be a better version of the changelog entry for this PR? If there should not be a changelog entry, we can definitely adjust, but if there should be something included, would you be able to clarify a bit what that would be?

Hi @kmartens27 thanks for the reminder - I have updated the suggested changelog entry.

• JENKINS-72796, Ensure threads in the Computer.threadPoolForRemoting executor service always have the Jenkins webapp ClassLoader set as the context ClassLoader to prevent random class loading issues when code is running in this ExecutorService.

[kmartens27]

Thank you so much!