RFR: 8323807: Async UL: Add a stalling mode to async UL [v6]

[Johan Sjölen]

On Wed, 22 May 2024 16:18:32 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

>> Hi,
>> 
>> This PR does two things for the asynchronous UL mode:
>> 
>> 1. Replaces the ping-pong buffers with a circular buffer.
>> 2. Adds a `stall` mode to async UL, ensuring that no messages are ever dropped if the log message producers out pace the log message writing thread.
>> 
>> These changes have been discussed on the hotspot-dev mailing list under the thread name "Request for Comment: Add a stalling mode to asynchronous UL". Xin Liu, the original author of the ping-pong approach, has confirmed that switching to circular buffers leads to a reduced rate of dropped messages.
>> 
>> The ticket description and my original e-mail contain approximately the same information and I'd recommend that you read either of those if you want an overview of why these changes are made and what the high-level protocol is.
>> 
>> All the best,
>> Johan
>
> Johan Sjölen has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 58 additional commits since the last revision:
> 
>  - Merge remote-tracking branch 'openjdk/master' into ul-async-producer-consumer-take2
>  - Merge remote-tracking branch 'origin/master' into ul-async-producer-consumer-take2
>  - Do not let go of producer lock when stalling
>  - Just inline it.
>  - TBIVM and small refactor
>  - Reflect renamings in tests
>  - Move more towards producer/consumer and fix alignment
>  - change to producer consumer in comment
>  - Rename to maybe_has_message
>  - Atomic::store for _tail/_head in locked methods
>  - ... and 48 more: https://git.openjdk.org/jdk/compare/30517338...0e87ea10

I'm not very happy with the details in this PR regarding the usage of wait/notify. I'm moving this into draft to avoid any more activity on the mailing lists (I think that's how it works?). I'll ping the pre-existing reviewers here when I'm happy with the new version.

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PR Comment: https://git.openjdk.org/jdk/pull/17757#issuecomment-2127764829