RFR: 8229517: Support for optional asynchronous/buffered logging [v10]

[Xin Liu]

On Mon, 3 May 2021 23:30:20 GMT, Xin Liu <xliu at openjdk.org> wrote:

>> This patch provides a buffer to store asynchrounous messages and flush them to
>> underlying files periodically.
>
> Xin Liu has updated the pull request incrementally with three additional commits since the last revision:
> 
>  - Implement the global option -Xlog:async per CSR.
>    
>    The old options -XX:+AsyncLogging and the output option are both removed.
>    This patch also deliver the zero-cost promise. ie. No AsyncLog thread will be
>    launched if async_mode is not eanbled.
>  - Reimplement Accurate Decorations for AsyncLogging.
>    
>    LogDecorations defines a copy constructutor. Each log message copys it
>    once.
>  - Revert "Accurate Decorations for AsyncLogging."
>    
>    This reverts commit 1f06be3126f829055aff3720aea7e82544fd0c3a.

Hi, Reviewers, 

May I ask to review this PR? I make it comply with the CSR. A global flag `-Xlog:async` will enable async logging. 
By default, this flag is off.  Now it's pure zero-cost by default.  HotSpot even doesn't launch asynclog thread. 

thanks,
--lx

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PR: https://git.openjdk.java.net/jdk/pull/3135