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

[Alan Bateman]

On Tue, 24 May 2022 19:36:02 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

>> I don't think it is correct to say that this command line option is a preview feature. Maybe it can be clarified on a second line:
>> 
>> 
>> -trackvthreads    track virtual threads as they are created
>>                              Virtual threads are a preview feature of the Java platform.
>
> Does that imply that `-trackvthreads` can be changed or removed?

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.

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