jcmd - executing multiple commands at the same safepoint?

[David Holmes]

On 13/05/2018 4:10 AM, Kirk Pepperdine wrote:
> 
>> 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.

Please do. That seems more likely to be incorrect reporting to me ... I 
seem to recall at least one still open issue in this area ...

Thanks,
David
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> 
>>
>>>
>>> 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
>