RFR: 8286983: Add mention of "Preview Feature" for new loom related jdb and debug agent options [v2]

[David Holmes]

On Wed, 25 May 2022 16:11:52 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

>> If virtual threads become permanent then the usage message would minimally be updated to drop the sentence that virtual threads are a preview feature. At that point the debugger APIs may have been built out further and it might be that there is no need for the -trackvthreads option but that's too far out to know at this point.
>> 
>> If virtual threads were to be removed then the -trackvthreads command line option would be removed too.
>
>> If virtual threads become permanent then the usage message would minimally be updated to drop the sentence that virtual threads are a preview feature.
> 
> But that's precisely the commitment to this flag that I want to avoid.  I want something that is the equivalent of `EXPERIMENTAL` for `-XX` flags.

Again I have to say I agree with Chris. The flag itself is a "preview" flag and relates to a "preview feature". If the feature goes obviously the flag does too, but the flag could go even if the feature stays.

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PR: https://git.openjdk.java.net/jdk/pull/8780