JDK-8177064: jcmd help command should not require the process identification

[David Holmes]

Hi Gary,

On 12/04/2019 4:24 am, Gary Adams wrote:
> Two years ago a request was made to allow
> 
>     jcmd help
> 
> to be interpretted as a request for help from the current jcmd process
> rather than requiring a separate target process to be involved.
> 
> Some attempts were made to close the issue, because the
> command was not documented to work that way.
> It was also pointed out that the help from the running jcmd
> might not match the cmds available from a subsequent
> request to a different process possibly running a different version
> of the vm.
> 
> As proof of concept exercise this webrev shows a minimal set of
> changes that could support
> 
>    jcmd self help
> 
> Before fleshing out additional changes in documentation and testing,
> I'd like to know if this is still a worth while enhancement. Also,

Given we allow a pid of 0 to mean all Java processes I can see scope for 
a special value that means "the current Java process", but using a text 
word like "self" seems awkward at best. Plus within a shell you can use:

jcmd $$ help

to act on the jcmd VM itself, so there doesn't need to be special 
treatment in that sense. Perhaps some tweaks to the "jcmd -h" text.

> I'd like to know more about the history of the checks preventing self 
> attach.

This may give you a start: https://bugs.openjdk.java.net/browse/JDK-8177154

Cheers,
David

>    Webrev: http://cr.openjdk.java.net/~gadams/8177064/webrev/index.html
>    Issue: https://bugs.openjdk.java.net/browse/JDK-8177064