> `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 one of "yyyy-MM-dd HH:mm:ss" format.
> 
> 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
>                         ^^^^
> 
> * The choice for time format is "yyyy-MM-dd HH:mm:ss" as it is already used 
> in `Thread.print`.
> * `Thread.print` prints timestamp irrespectively from "-T" flag presence to 
> preserve backwards compatibility.
> 
> I haven't added a timestamp to the following diagnostic command:
> * `VM.uptime` - command run with `-date` argument will also print a timestamp;
> * `VM.system_properties` - as the output already lists a timestamp. Not sure 
> if we need more timestamps here.
> * `Thread.dump_to_file` - the content dumped to a file already has a 
> timestamp;

Ivan Bereziuk has updated the pull request incrementally with one additional 
commit since the last revision:

  change flag name from -T to -t

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/27368/files
  - new: https://git.openjdk.org/jdk/pull/27368/files/c702901d..f0e39a34

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27368&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27368&range=02-03

  Stats: 13 lines in 6 files changed: 0 ins; 0 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/27368.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27368/head:pull/27368

PR: https://git.openjdk.org/jdk/pull/27368

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