RFR: 8323807: Async UL: Add a stalling mode to async UL [v3]

[Johan Sjölen]

> 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 eight additional commits since the last revision:

 - Atomic::store for _tail/_head in locked methods
 - Prepend _ to private members head/tail
 - Rename calc_mem
 - Rename used/unused pairing
 - Style nit
 - Use Consumer/Producer terminology for Locker classes
 - Use explicit global calls
 - Shorten

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/17757/files
  - new: https://git.openjdk.org/jdk/pull/17757/files/8c4ced0f..c51a679c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17757&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17757&range=01-02

  Stats: 46 lines in 4 files changed: 3 ins; 0 del; 43 mod
  Patch: https://git.openjdk.org/jdk/pull/17757.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17757/head:pull/17757

PR: https://git.openjdk.org/jdk/pull/17757