jcmd - executing multiple commands at the same safepoint?

[Martin Skarsaune]

Hi Thomas,

very positive suggestion.

One observation:
There already seems to be some different interpretation of the command line
in different Java versions:
For instance when I try to dump a flight recording in 1.8.0_152-ea-b05 : I
can use:
jcmd 33014 JFR.dump filename="recording1.jfr" recording=1
but in build 9+181 , the same command must be:
jcmd 33014 JFR.dump filename="recording1.jfr",recording=1
(the comma to separate sub-options you mentioned earlier)

Therefore the suggestion without curly brackets, giving several commands
after one another seems good with regard to backwards compatibility.

Motivation: hawt.io uses the
MBean com.sun.management:type=DiagnosticCommand to access the same
functionality as jcmd. Variations in option syntax across Java versions is
already an issue (only affecting sub-options though, as each command is a
separate JMX operation). So syntax compatibility is highly appreciated :-)

Martin

lør. 12. mai 2018 kl. 20:11 skrev Kirk Pepperdine <kirk.pepperdine at gmail.com
>:

>
> > On May 10, 2018, at 11:26 AM, Thomas Stüfe <thomas.stuefe at gmail.com>
> wrote:
> >
> > On Thu, May 10, 2018 at 9:13 AM, Kirk Pepperdine
> > <kirk.pepperdine at gmail.com> wrote:
> >> The stacking at the safe point would be a huge win. Right now thread
> dump consistency can really confuse people as the tooling will show two
> threads owning the same lock at seemingly the same time. Reality, it’s just
> that people didn’t realize you get a safe point for each thread therefor
> there is motion in the system as you’re collecting the data.
> >
> > I am a bit confused. What tooling are you talking about?
>
> jstack. I’ve not seen it with jcmd. But I often see 2 threads holding the
> same lock at the “same time” which is of course non-sense. I can dig one up
> for you if you’re still confused.
>
>
> >
> >>
> >> As an aside, it’s amazing how many dev’s aren’t aware of jcmd. Just
> yesterday after my session at Devoxx I had someone ask me about using jfr
> from the command line, many in that session had not seen jcmd before. The
> feedback was, wow, this is very useful and I wished I had of known about it
> earlier.
> >
> > Yes, jcmd is quite useful. I also really like the simple design, which
> > is by default up- and downward compatible (so you can talk to any VM,
> > new, old, it should not matter). That is just good design. We - Sap -
> > work to extend jcmd, to help our support folks. E.g. the whole new
> > VM.metaspace command chain.
>
> And simple it is….well done!!!
>
> — Kirk
>
>
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