RFR (M) 8223456: CSR Delayed starting of debugging via jcmd

[Volker Simonis]

Hi Alan,

you may be right that the initial submitter and reviewers have missed
the need of a CSR, but after all, the change itself has been correctly
reviewed on serviceability-dev by your colleague Chris Plummer and my
colleague Christoph Langer. I think it is a little exaggerated to
claim the backout of a change which has been pushed almost 6 month ago
and didn't do any harm until now, just because of a missing CSR. Such
mails really demotivate new committers who did their best in order to
contribute to OpenJDK.

I agree that "onjcmd" may not be an optimal description for the flag.
I would suggest to use "ondemand" but we can discuss that on the
corresponding CSR thread. In general the change is just a part of our
effort to contribute our "Debugging on Demand" feature [1] from SAP
JVM to the OpenJDK. We have already contributed some parts [2] and
another major part (making Escape Analysis in C2 work together with
debugging) is just about to be contributed. For our proprietary SAP
JVM we had a special tool called "jvmmon" which is similar to "jcmd"
and which could be used to connect to a running VM and start a
debugging session at any time. For OpenJDK it seemed naturally to
implement this functionality in "jcmd".

I don't understand what problem you see when saying that this feature
"ties the debugger agent to a unrelated JDK-specific tool". The
debugger agent already has quite some implementation and platform
specific dependencies like different connectors and transports for
example. Moreover the "Debugging on Demand" feature isn't really tied
to one specific tool like "jcmd" (although the unfortunate option
naming "onjcmd" may suggest that). But if you read "8223456: Delayed
starting of debugging via jcmd" [3] carefully, you'll see that other
tools like "jconsole" or even another Java program using the
DiagnosticCommandMBean can be used just as well.

I hope we can all work together in good faith and without threats to
bring this feature, which has proved to be extremely useful and
popular among our customers, into the OpenJDK. We are of course open
for any constructive suggestion which further improve this feature.

Best regards,
Volker

[1] https://help.sap.com/doc/saphelp_nwmobile71/7.1.18/en-US/80/3f7a2244814aad8b4a09e1c2e7629b/content.htm?no_cache=true
[2] https://github.com/SAP/SapMachine/wiki/Features-Contributed-by-SAP#debugging-on-demand
[3] https://bugs.openjdk.java.net/browse/JDK-8223456

On Mon, May 27, 2019 at 3:45 PM Alan Bateman <Alan.Bateman at oracle.com> wrote:
>
> On 27/05/2019 14:23, Schmelter, Ralf wrote:
>
> I need reviews for the following CSR: https://bugs.openjdk.java.net/browse/JDK-8223456
>
> Note that this CSR is for a feature which already was commited to JDK 12.
>
>
> I think this feature needs to be re-examined, maybe backed out or the onjcmd sub-option hidden from the help output if we can't get agreement before JDK 13 RDP1. It's unfortunate that it was pushed to JDK 12 without a CSR because that would have been the opportunity to ask questions. The problem with this feature is that it ties the debugger agent to a unrelated JDK-specific tool. It feels like it conflates two things.  So I think the "feature" needs to be re-discussed to see whether the scenario is really compelling and to see the list of alternatives that were explored.
>
> -Alan