`jcmd` provides great diagnostics but many commands lack a timestamp in their
output.
Adding a timestamp to the output of some would add value for those debugging
JVM data.
With this MR I propose to introduce time-stamping to all diagnostic `jcmd`
commands in a form of an additional common flag "-T":
jcmd [pid | main-class] [-T] command... | PerfCounter.print | -f filename
^^^^
This is a simplified approach to handle timestamp (v1 is
[here](https://github.com/openjdk/jdk/pull/27368))
Some diagnostic commands already provide timestamps information. For example
`Thread.print` already starts with a timestamp of "yyyy-MM-dd HH:mm:ss" format.
In that case the timestamp is printed twice if "-T" flag is passed to
`Thread.print`.
-------------
Commit messages:
- improve TestJcmdTimestamp.java. add '-f <file>
- implementation v2, top level timestamping
- remove TimeStamp::No as it's not used. virtual should be flipped to override
in bulk (afressed clang warning)
- Merge branch 'master' into 8357828_add_timestamp_to_jcmd
- changes to jcmd.md
- undo changes to reorder_help_cmd()
- cleanup
- add timestamp to VM.version. Add test
- updated jcmd usage text
- undo the changes to the modified earlier tests as timestamp presence is
fully backwards compatible
- ... and 7 more: https://git.openjdk.org/jdk/compare/f2d5290c...eaea764d
Changes: https://git.openjdk.org/jdk/pull/29325/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29325&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8357828
Stats: 189 lines in 6 files changed: 169 ins; 4 del; 16 mod
Patch: https://git.openjdk.org/jdk/pull/29325.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/29325/head:pull/29325
PR: https://git.openjdk.org/jdk/pull/29325
