RFR: 8323807: Async UL: Add a stalling mode to async UL

[Johan Sjölen]

On Wed, 7 Feb 2024 20:24:31 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

Some irrelevant G1 test failures so far.

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PR Comment: https://git.openjdk.org/jdk/pull/17757#issuecomment-2010054674