RFR: 8323807: Async UL: Add a stalling mode to async UL [v5]

[Johan Sjölen]

On Tue, 2 Apr 2024 14:41:27 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 incrementally with one additional commit since the last revision:
> 
>   TBIVM and small refactor

There are some issues with regards to the possibility of starvation in the stalling mode. I am working on sorting this out.

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PR Comment: https://git.openjdk.org/jdk/pull/17757#issuecomment-2038363174