RFR: 8259070: Add jcmd option to dump CDS [v12]

[Hamlin Li]

On Wed, 14 Apr 2021 19:08:25 GMT, Yumin Qi <minqi at openjdk.org> wrote:

>> Hi, Please review
>> 
>>   Added jcmd option for dumping CDS archive during application runtime. Before this change, user has to dump shared archive in two steps: first run application with
>>   `java -XX:DumpLoadedClassList=<classlist> .... `  
>>  to collect shareable class names and saved in file `<classlist>` , then 
>>   `java -Xshare:dump -XX:SharedClassListFile=<classlist> -XX:SharedArchiveFile=<archivefile> ...`
>>   With this change, user can use jcmd to dump CDS without going through above steps. Also user can choose a moment during the app runtime  to dump an archive.
>>    The bug is associated with the CSR: https://bugs.openjdk.java.net/browse/JDK-8259798 which has been approved.
>>    New added jcmd option:
>>    `jcmd <pid or AppName> VM.cds static_dump <filename>`
>>    or
>>     `jcmd <pid or AppName> VM.cds dynamic_dump <filename>`
>>   To dump dynamic archive, requires start app with newly added flag `-XX:+RecordDynamicDumpInfo`, with this flag, some information related to dynamic dump like loader constraints will be recorded. Note the dumping process changed some object memory locations so for dumping dynamic archive, can only done once for a running app. For static dump, user can dump multiple times against same process. 
>>    The file name is optional, if the file name is not supplied, the file name will take format of `java_pid<number>_static.jsa` or `java_pid<number>_dynamic.jsa` for static and dynamic respectively. The `<number>` is the application process ID.
>> 
>>   Tests: tier1,tier2,tier3,tier4
>> 
>> Thanks
>> Yumin
>
> Yumin Qi has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Removed extra assert and fixed extra Path usage in test

Marked as reviewed by mli (Reviewer).

I looked back at the history, and find out why it calls from JVM into java then into JVM again, nice solution!

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PR: https://git.openjdk.java.net/jdk/pull/2737