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From Steve Poole <spoole...@googlemail.com>
Subject Re: Do we need to change the scope of the API design?
Date Fri, 27 Nov 2009 09:33:40 GMT
On Thu, Nov 26, 2009 at 5:02 AM, Bobrovsky, Konstantin S <
konstantin.s.bobrovsky@intel.com> wrote:

> Hi Steve,
>
> I think the first option would be ideal of course. But I assume the
> initiative to develop RI based on Sun's Serviceability Agent (which would
> lower the implementation cost dramatically) has failed because of
> GPL-related issues. I wish there was a volunteer from the open-source who
> could adapt SA to the KATO API...
>
> That would be nice Konst. To be honest though, if I was wishing for help
like this I would prefer to have someone work with us on creating the
extended JVMTI or new C API interface as I wrote about previously.    The
runtime restrictions on the SA really effect it's usefulness for end users
of our API.     The cost of writing a corefile reader for hotspot is also
quite large - it could easily take someone 6 months to write or more.
Therefore I'd rather be pragmatic about this and focus on what can be done
by us and what people say they want.

>From the other two, the second one (remove Image API) IMO would very much
> discord with the original message of the JSR (*postmortem* analysis, which
> means digging through the core dumps). So I'd vote for leaving as much as
> possible of the Image API in the spec, making parts optional as needed.
>

I understand about changing the message but I feel uncomfortable to say the
least to have a large part of our API not supported by the Reference
Implementation.    I will put together a proposal and explain what I think
needs to be done.

You can look at this from anoher point of view.   We know that core file
sizes are rising ( 8-30GB production heap sizes are now common) and we
agreed thereforet at some point core files would become untenable.   That's
why we have the "snapshot" api  idea.  It seems that for most people the
usefulness of corefiles is already in doubt so  lets focus on producing a
new modern dump mechanism that is fast, scaleable,  content configurable
and generally cross JVM.   Since we will be developing a reference
implementation to go with the design we will effectively be producing a
modern replacement for HPROF and since the format for this dump is not part
of the specification (as we have agreed that data formats are always
constraining) we will not get rocks thrown at us by JVM vendors who want to
implement their own alternatives.

I think developing the HPROF alternative is the right place to go.  Users
will understand the concept and we might actually gain input from existing
HPROF users who want to see improvements made.

We are building the current implementation just using JVMTI.  Thats not good
enough and we need to find ways of getting more data out of a JVM.  Hence
the idea of improving JVMTI or adding some new API.     That is probably not
the right way either but lets discuss..


> Thanks,
> Konst
>
> Intel Novosibirsk
> Closed Joint Stock Company Intel A/O
> Registered legal address: Krylatsky Hills Business Park,
> 17 Krylatskaya Str., Bldg 4, Moscow 121614,
> Russian Federation
>
>
> >-----Original Message-----
> >From: Steve Poole [mailto:spoole167@googlemail.com]
> >Sent: Wednesday, November 25, 2009 7:44 PM
> >To: kato-spec@incubator.apache.org
> >Subject: Do we need to change the scope of the API design?
> >
> >Stuart's note on diagnosing JNI problems (thanks for the review Stuart)
> has
> >touched on a key point  concerning what we want to do and what we can do.
> >
> >I think its time we discuss where we are and what happens next.
> >
> >Our desire to specify an API that helps people solve problems has to be
> >tempered with  practical implementation considerations.   The API design
> >that IBM contributed to the Kato project is satisfiable by IBM JVMs (of
> >course),  but for us to develop a matching reference implementation we
> know
> >now that we need to get much more information from the Sun JVM than we
> have
> >today.  Developing a full solution to match the API as it stands today is
> >difficult for the Kato project as the code we would need to access is in
> >OpenJDK and is under the GPL.
> >
> >Practically, we have few choices.  We could
> >
> >1 - Get a JVM Vendor to produce , or commit to produce  an implementation
> >that fully covers the Image API side.
> >2 - Remove all the Image API side from the design
> >3 - Find a halfway point where some of the Image API stays and is
> optional.
> >
> >I've had many conversations with people concerning option 1 and the
> >response
> >is generally that its too expensive for the potential return.  Both for
> >implementation and ongoing maintenance.
> >
> >Option 2 seems very draconian -  the ability to get at some of the native
> >information (such as the native thread for a Java thread) just seems too
> >useful to remove.
> >
> >I'd opt for us moving the API design towards option 3 - there are some
> >basic
> >changes we could do such as extracting the native access methods into a
> >separate interface and allowing the implementer the choice to use it.
> >
> >We still need to get access to more data from the JVM (and perhaps in
> >better
> >ways) than we have today.  We need to get this data in such a manner as
> not
> >to require accessing GPL code and in a way that is cheap to maintain as
> the
> >JVM evolves.
> >
> >My idea for resolving this conundrum is to propose that we include in our
> >API design either a new JVM 'C' API or  extensions to JVMTI. We would not
> >implement these additions in the RI but would rely on others to provide an
> >implementation.  (We would design the RI and the API to make this extra
> >information optional)
> >
> >Comments?
> >
> >
> >--
> >Steve
>



-- 
Steve

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