RFR: 8323807: Async UL: Add a stalling mode to async UL [v2]

[Johan Sjölen]

On Wed, 20 Mar 2024 17:05:49 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 41 additional commits since the last revision:
> 
>  - Merge remote-tracking branch 'origin/master' into ul-async-producer-consumer-take2
>  - Missing N
>  - Move constructors out of header file
>  - Style
>  - Correctly implement stalling
>  - Missed one
>  - Fix lossy conversions in tests
>  - Merge remote-tracking branch 'origin/master' into ul-async-producer-consumer-take2
>  - Only include sys/mman on Linux
>  - Revert back to original Linux impl
>  - ... and 31 more: https://git.openjdk.org/jdk/compare/642d8779...8c4ced0f

@tstuefe , @navyxliu, @dholmes-ora 

Hi,

I've set up this PR for staling mode in UK. If you do have the time and interest, then I would very much appreciate a review to get this feature in.

I'm waiting until the PR is in shape before I do any man page updates.

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PR Comment: https://git.openjdk.org/jdk/pull/17757#issuecomment-2020491432