[8u] RFR 8233197: Invert JvmtiExport::post_vm_initialized() and Jfr:on_vm_start() start-up order for correct option parsing

[Mario Torre]

Il giorno mer 10 giu 2020 alle ore 18:21 Andrey Petushkov
<andrey at azul.com> ha scritto:
>
> Just in case, starting a recording in pre-main works flawlessly with the
> current state of the code (in fact AFAICT recording which is started via
> command line is in fact started earlier than agent's premain is executed)

You mean with Jaroslav's patch?

Cheers,
Mario

> And yes, it's typical use-case that that JFR is not activated on the
> command line but some time later the recording is requested with
> jcmd/JMC/JMX. In this it's enabled via management
>
> Andrey
>
> On 10.06.2020 19:05, Mario Torre wrote:
> > Doesn’t that create an issue when JFR is not started but then enabled at
> > runtime via the agent?
> >
> > So far the only use case for this was attaching via JMX but an agent could
> > still request JFR, I’m not sure if creating a recording in pre-main is a
> > legal use case or not though.
> >
> > Btw, this patch has been backported in 11 and 13 without this level of
> > discussion, I guess we should revisit those patches too at this point.
> >
> > Cheers,
> > Mario
> >
> > On Wed 10. Jun 2020 at 17:48, Andrew Dinn <adinn at redhat.com> wrote:
> >
> >> On 10/06/2020 13:31, Jaroslav Bachorík wrote:
> >>>> 3505 #if INCLUDE_JFR
> >>>> 3506     // The VM creates & returns objects of this class. Make sure
> >> it's initialized.
> >>>> 3507     initialize_class(vmSymbols::java_lang_Class(), CHECK_0);
> >>>> 3508 #endif
> >>>>
> >>>> ISTM that this code is run unconditionally if INCLUDE_JFR is set at
> >> compile
> >>>> time. Am I misunderstanding something?
> >>> Ok. I misunderstood the original request. I thought it was supposed to
> >>> be in-line with other JFR specific changes which are guarded with
> >>> compile-time conditional blocks.
> >>>
> >>>> If this is not true, and the initialize_class only runs if JFR is
> >>>> enabled, how does that work?
> >>> This thing you ask (runtime check for whether JFR is enabled) is
> >>> impossible at that place, AFAIK. The affected code is in 'create_vm'
> >>> block so JVM is not really alive. Checking the JFR enabled status
> >>> requires parsing JFR configs which happens to be done in Java and that
> >>> requires java.lang.Class to be already linked and initialized - making
> >>> it impossible to check the JFR enablement status before initializing
> >>> java.lang.Class.
> >> How is that so? I believe command line arguments will have been
> >> processed at this stage. If so then you can easily detect whether or not
> >> JFR has been enabled on the command line. The simplest thing is to check
> >> global boolean FlightRecorder. This global is set from the command line
> >> using -X:+FlightRecorder and cleared using -X:-FlightRecorder. If not
> >> specified it defaults to false.
> >>
> >> So, in the case where JFR is conditionally compiled in you can call
> >> initialize_class() early if FlightRecorder is true and call it at the
> >> normal point of FlightRecorder is false.
> >>
> >> In the case where JFR is conditionally compiled out then the call should
> >> happen late as happened before this patch.
> >>
> >> Is there any reason why that won't work?
> >>
> >> regards,
> >>
> >>
> >> Andrew Dinn
> >> -----------
> >> Senior Principal Software Engineer
> >> Red Hat UK Ltd
> >> Registered in England and Wales under Company Registration No. 03798903
> >> Directors: Michael Cunningham, Michael ("Mike") O'Neill
> >>
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> > Java Champion - Blog: http://neugens.wordpress.com - Twitter: @neugens
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Java Champion - Blog: http://neugens.wordpress.com - Twitter: @neugens
Proud GNU Classpath developer: http://www.classpath.org/
OpenJDK: http://openjdk.java.net/projects/caciocavallo/

Please, support open standards:
http://endsoftpatents.org/