RFR: 8282225: GHA: Allow one concurrent run per PR only [v2]

[Magnus Ihse Bursie]

On Tue, 22 Feb 2022 16:18:24 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Since last year, GHA allows concurrency control over GHA runs:
>>  https://github.blog/changelog/2021-04-19-github-actions-limit-workflow-run-or-job-concurrency/
>>  https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#concurrency
>> 
>> Our GHA workflows trigger on every PR update, sometimes doing multiple runs per PR. This is seldom useful and wastes resources with our very large jobs. For example, one can push a commit, quickly realize there is a mistake, push another commit, and this would do *two* GHA runs, both taking many hours.
>> 
>> I think we can say that only one run per branch is good, and all running/pending runs should be cancelled when a new run starts.
>> 
>> Additional testing:
>>  - [x] Verified queued run gets cancelled on new commit
>>  - [x] Verified in-progress run gets cancelled on new commit
>>  - [x] Verified in-progress run gets cancelled on merge
>>  - [x] Verified in-progress run gets cancelled on rebase + force-push
>
> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Also specialize by workflow

Of course, the more the merrier. :-) Especially if you are making a big or controversial change, it's good to wait for more reviewers. It's also good to wait for reviewers from the build group (sometimes developers from other teams approve build changes, but they might miss subtleties). But if you think that one reviewer is enough, you don't really need to ask permission to integrate with just one reviewer.

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PR: https://git.openjdk.java.net/jdk/pull/7570