8357828: Add a timestamp to jcmd diagnostic commands

[Domest0s]

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.

Some diagnostic commands already provide timestamps. For example Thread.print already prints timestamp in a "yyyy-MM-dd HH:mm:ss" format.

Adding timestamps to all diagnostic jcmd commands with a non-throw-away STDOUT.

The exceptions are:

• VM.uptime - command run with -date argument will also print a timestamp;
• VM.system_properties - already lists timestamp
• Thread.dump_to_file - the content dumped to file already has a timestamp;
• VM.version

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Progress

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Issue

• JDK-8357828: Add a timestamp to jcmd diagnostic commands (Enhancement - P4)

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[AlanBateman]

I assume you didn't mean to print a time stamp here as the output already has a timestamp. Also for -format=json and sending the output to stdout, then it will be unparsable if a timestamp appears before the JSON object.

[Domest0s]

Hi Alan. That's right.
My mistake. I declared the intention to not have timestamps for commands with a throwaway stdout. This also includes "Thread.dump_to_file" command but then mistakenly added print_local_time() in here.

[mlbridge]

Webrevs

• 00: Full (bfa2a927)

[Domest0s]

Internal testing tier 1-5 did not show any issues.