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From Mark Hindess <mark.hind...@googlemail.com>
Subject Re: Question about the boot and classloading
Date Tue, 19 May 2009 21:06:57 GMT

In message <e0f125db0905190627l72e6894fuc6904e92f37c27d4@mail.gmail.com>,
Pavel Pervov writes:
>
> Please, read this nice presentation [1] on osgi vs classic class loading.
> [1] http://www.martinliqert.com/events/WJAX2008-ClassloadingTypeVisibilityOSGi.pdf

I assume you mean:

  http://www.martinlippert.org/events/WJAX2008-ClassloadingTypeVisibilityOSGi.pdf

-Mark.

> 2009/5/19, tian galaxy <harmonymail.ty@gmail.com>:
> > XiaoFeng , Mark
> > Thanks for your help ,very valuable to me.
> > I think I need to research more on this .Much more complex than I thought
> > previously.
> >
> >
> > Regard
> > Tian
> >
> > 2009/5/19 Xiao-Feng Li <xiaofeng.li@gmail.com>
> >
> >> On Tue, May 19, 2009 at 6:41 PM, Mark Hindess
> >> <mark.hindess@googlemail.com> wrote:
> >> >
> >> > In message
> >> > <dff214c70905190147x57135ef3hf26cbf6a93ae2255@mail.gmail.com>,
> >> tian
> >> > galaxy writes:
> >> >>
> >> >> Hindess .Thanks for the help ! I realized that this far more complex
> >> than I
> >> >> thought before .
> >> >> So I think I need a deeper look into both osgi and harmony .
> >> >> Here are several things I don't qiute understand and I noted them
> >> below.May
> >> >> be it's because I am not quite familiar with the low level ,
> >> classloading
> >> >> details .
> >> >> thanks!
> >> >>
> >> >> 2009/5/19 Mark Hindess <mark.hindess@googlemail.com>
> >> >> >
> >> >> > In message <
> >> dff214c70905180610w407e3bd4h5baa319729c1fc55@mail.gmail.com>,
> >> >> > tian galaxy writes:
> >> >> > >
> >> >> > > OK ,thanks .Seems the minimal class set has been defined
by the
> >> osgi.
> >> >> >
> >> >> > Not sure how this helps though.  The OSGi Minimum Execution
> >> Environment
> >> >> > says what is theoretically the minimum required to run OSGi. 
What we
> >> >> > need to concern ourselves with is the *practical* minimum and
that
> >> >> > really depends on our implementation details.
> >> >> >
> >> >> > I don't think that we should implement OSGi in the VM.  Instead
the
> >> >> > existing bootstrap classloader should load the OSGi framework
(with
> >> >> > a unique classloader)
> >> >>
> >> >> If we load the osgi with the bootstrap class loader , why comes a
> >> >> unique
> >> >> class loader?
> >> >
> >> > It isn't necessary but I think it is useful to use a separate
> >> > classloader for the OSGi framework so that we can isolate the classes
> >> > use by the VM's OSGi framework and avoid polluting the namespace.
> >> >
> >> >> Do you mean the bootstrap class loader should delegate the loading
to
> >> >> the 'unique class loader '?
> >> >
> >> > Yes.
> >> >
> >> >> > and the system classes (with a "temporary" classloader).
> >> >>
> >> >> Again ,the relation between temporary and bootstrap classloder?  And
> >> >> why temporary ?
> >> >
> >> > Temporary because until the OSGi framework is up you wont know which
> >> > bundle the classes belong to and thus wont know which bundle classloader
> >> > the classes should belong to.  Alternatively, I suppose you could
> >> > implement minimal support for reading OSGi headers from manifests
> >> > in the VM so that you could assign classes to what would become a bundle
> >> > classloader when the framework is up.
> >> >
> >> > -Mark.
> >>
> >>
> >> This makes sense to me. The VM simply grabs in all the stuff "as
> >> usual" including the OSGi framework, then sort them out according to
> >> the bundles' definitions.
> >>
> >> It could be VM-neutral, because it is the VM's own business to take
> >> care of its loaded classes. A callback interface OSGI_ready() can
> >> inform the VM to tidy up the classes loaded for OSGi (or before it is
> >> ready).
> >>
> >> Thanks,
> >> xiaofeng
> >>
> >>
> >> >> >  Once the OSGi framework is configured the system classes need
to be
> >> >> > moved to the correct classloader for the OSGi bundle to which
they
> >> >> > belong.
> >> >> >
> >> >> > This means that during the initial starting-OSGi-framework phase
> >> >> > the OSGi bundle import/exports will not be enforced but, other
than
> >> >> > implementing OSGi in the VM, I don't see how to avoid this.
> >> >> >
> >> >> > The multiplicity of bootstrap classloaders still needs to be hidden
> >> >> > since the API demands that getClassLoader should return null for
the
> >> >> > bootstrap classloader(s).
> >> >> >
> >> >> > The biggest problem is probably how to implement this as
> >> VM-independent
> >> >> > API such that a VM wanting to implement OSGi had to provide only
a
> >> >> > minimal C/Java interface in order to gain OSGi support.
> >> >> >
> >> >> > Regards,
> >> >> >  Mark.
> >> >> >
> >> >> > > I will look more closely on this problems and let you know
if there
> >> some
> >> >> > > progresses made.
> >> >> > > Thanks  a  lot !
> >> >> >
> >> >> > > 2009/5/18 Pavel Pervov <pmcfirst@gmail.com>
> >> >> > >
> >> >> > > > I do not know osgi model in detail, but what minimal
set of
> >> classes is
> >> >> > > > needed to start osgi model itself? Then we could delegate
to
> >> "system"
> >> >> > > > bundle loader from bootstrap classloader.
> >> >> > > >
> >> >> > > > 2009/5/18, tian galaxy <harmonymail.ty@gmail.com>:
> >> >> > > > > Yes , implement osgi loading model in there is
too complex.
> >> >> > > > >
> >> >> > > > > We know some modules are more important than others
,
> >> >> > > > > performing
> >> some
> >> >> > > > > fundamental , basic functions .
> >> >> > > > > Is it possible to only load these more" basic "
modules with
> >> >> > bootstrap
> >> >> > > > class
> >> >> > > > > loader and make the other modules work the osgi
bundle?
> >> >> > > > > Actually I don't quite understand why system classes
could only
> >> be
> >> >> > loaded
> >> >> > > > by
> >> >> > > > > bootstrap class loader?I noticed that there are
some safety
> >> concerns
> >> >> > > > > ,is there any reasons other than that?
> >> >> > > > > Thanks !
> >> >> > > > >
> >> >> > > > >
> >> >> > > > > 2009/5/18 Pavel Pervov <pmcfirst@gmail.com>
> >> >> > > > >
> >> >> > > > >> Short answer is "no". You'll have to implement
osgi loading
> >> model
> >> >> > > > >> inside bootstrap classloader. Is it too complex?
> >> >> > > > >>
> >> >> > > > >> 2009/5/18, tian galaxy <harmonymail.ty@gmail.com>:
> >> >> > > > >> > Hi Pavel.
> >> >> > > > >> >
> >> >> > > > >> > Thanks.
> >> >> > > > >> > Yes ,that's right .My question is whether
there is a way to
> >> load
> >> >> > the
> >> >> > > > >> system
> >> >> > > > >> > class by class loader other than the 
bootstrap class loader
> >> ?
> >> >> > > > >> > If we could load the system class by different
loaders other
> >> than
> >> >> > the
> >> >> > > > >> > bootstrap class loader then there is a
chance to make the
> >> harmony
> >> >> > > > >> > runtime
> >> >> > > > >> to
> >> >> > > > >> > be osgi-ed.
> >> >> > > > >> > I trying to work on this problem . Do
you have any
> >> suggestions ?
> >> >> > > > >> >
> >> >> > > > >> >
> >> >> > > > >> > 2009/5/18 Pavel Pervov <pmcfirst@gmail.com>
> >> >> > > > >> >
> >> >> > > > >> >> Tian,
> >> >> > > > >> >> System classes are all loaded with
bootstrap classloader.
> >> >> > > > >> >> It
> >> is
> >> >> > > > >> >> written in C++ and is located in
> >> >> > > > >> >> working_vm/vm/vmcore/src/class_support/classloader.cpp
> >> >> > > > >> >>
> >> >> > > > >> >> 2009/5/17, tian galaxy <harmonymail.ty@gmail.com>:
> >> >> > > > >> >> > Hi all
> >> >> > > > >> >> > I have a question about the classloading
in the drlvm.
> >> >> > > > >> >> >
> >> >> > > > >> >> > I know that there are kernel
library inside the drlvm
> >> >> > > > >> >> > such
> >> as
> >> >> > > > >> >> > java.lang.classloader, which
enclose the the
> >> systemclassloader.
> >> >> > And
> >> >> > > > >> this
> >> >> > > > >> >> > class is loaded and used in the
process of creating VM .
> >> >> > > > >> >> > While the systemclassloader is
a subtype of
> >> >> > > > >> >> > urlclassloader
> >> >> > which is
> >> >> > > > >> >> > in
> >> >> > > > >> >> the
> >> >> > > > >> >> > "luni" module.So does the JNI_CreateJavaVM
> >> >> > > > >> >> > also load the urlclassloader
in the boot procedure of vm
> >> ?(I
> >> >> > failed
> >> >> > > > >> >> > to
> >> >> > > > >> >> > search related code in the source
code of drlvm).
> >> >> > > > >> >> > If so , when ?Before or after
the jni available ?
> >> >> > > > >> >> > Since I am trying to implement
the osgi on harmony and
> >> >> > > > >> >> > the
> >> osgi
> >> >> > > > works
> >> >> > > > >> >> with
> >> >> > > > >> >> > bundles (modules) , I think I
need to know the procedure
> >> of
> >> >> > booting
> >> >> > > > >> and
> >> >> > > > >> >> > loading of class from different
modules at the start up
> >> time.
> >> >> > > > >> >> > Any clue about this ?Thanks
> >> >> > > > >> >> >
> >> >> > > > >> >> > plus,do we have the source code
of java.exe ?Where?
> >> >
> >> >
> >> >
> >>
> >>
> >>
> >> --
> >> http://people.apache.org/~xli
> >>
> >
> >
> >
> > --
> > Regards
> > Michael Tian
> >
> 



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