Oops, sorry, misprinted in my suggestion:
if (cl->IsBootstrap() *||
*env->b_VTable_trace_is_not_supported_by_GC)
{
vm_enumerate_jlc(c);
if (c->vtable)
vm_enumerate_root_reference((void**)&c->vtObj,
FALSE);
}
Aleksey.
On 11/1/06, Aleksey Ignatenko <[EMAIL PROTECTED]> wrote:
Weldon,
>A question for all involved. Is it possible to somehow make it appear
that
>the new objects related to unloading (VTable, ClassLoader, etc) are
always
>reachable and thus never collected? I am trying to figure out a way to
make
>integration of class unloading independent of correct support inside the
GC
>and JIT. This option could be a command line switch or compile time
option.
I agree with Robin:
>Simple. Keep a list or table of these objects as part of the root set.
>Enumerate it optionally depending on a command line option.
Details: you can see from Harmony-2000 patch, that this is done for
Bootstrap classes already. If you look at root_set_enum_common.cpp (with the
patch applied) vm_enumerate_static_fields() function, there is line:
if (cl->IsBootstrap())
{
vm_enumerate_jlc(c);
if (c->vtable)
vm_enumerate_root_reference((void**)&c->vtObj,
FALSE);
}
else
{
vm_enumerate_jlc(c, true/*weak*/);
}
You can see, that there are strong roots to Bootstrap j.l.Classes and
their VTable objects. So I suppose, that it would be very simple to
propogate strong roots to all other classes (not only Bootstrap), something
like:
if (cl->IsBootstrap() *&&
env->b_VTable_trace_is_not_supported_by_GC*)
{
vm_enumerate_jlc(c);
if (c->vtable)
vm_enumerate_root_reference((void**)&c->vtObj,
FALSE);
}
where *b_VTable_trace_is_not_supported_by_GC *is flag which is set
according to used GC. This will force switching off any class unloading
support.
Aleksey.
On 11/1/06, Robin Garner <[EMAIL PROTECTED]> wrote:
>
> Weldon Washburn wrote:
> > On 10/30/06, Robin Garner <[EMAIL PROTECTED] > wrote:
> >>
> >> Weldon Washburn wrote:
> >> > On 10/27/06, Geir Magnusson Jr. <[EMAIL PROTECTED]> wrote:
> >> >>
> >> >>
> >> >>
> >> >> Weldon Washburn wrote:
> >> >> > Steve Blackburn was in Portland Oregon today. I mentioned the
> idea
> >> of
> >> >> > adding a reference pointer from object to its j.l.Classinstance.
> >> >> MMTk
> >> >> > was
> >> >> > not designed with this idea in mind. It looks like you will
> need to
> >> >> fix
> >> >> > this part of MMTk and maintain it yourself. Steve did not seem
> >> >> thrilled
> >> >> at
> >> >> > adding this support to MMTk code base.
> >>
> >> Actually I think the answer may have been a little garbled along the
> way
> >> here: MMTk is not a memory manager *for* Java, it is simply a memory
> >> manager. We have been careful to eliminate language-specific
> features
> >> in the heap that it manages. MMTk has been used to manage C# (in the
> >> Rotor VM) and was being incorporated into a Haskell runtime until I
> ran
> >> out of time.
> >>
> >> Therefore, MMTk knows nothing about the concept of class unloading,
> or
> >> java.lang.Class.
> >>
> >> >> How does MMTk support class unloading then?
> >> >
> >> >
> >> > MMTk has no special support for class unloading. This may have
> >> > something to
> >> > do with the entire system being written in Java thus class
> unloading
> >> come
> >> > along for free. If there needs to be a modification to support
> special
> >> > case
> >> > objects in DRLVM, someone will need to fixup MMTk and provide
> onging
> >> > support of this patch in Harmony. I have zero idea how big this
> effort
> >> > would be. It would also be good to hear what the impact will be
> on
> >> GCV5.
> >>
> >> MMTk implements several algorithms for retaining the reachable
> objects
> >> in a graph and recycling space used by unreachable ones. It relies
> on
> >> the host VM to provide a set of roots. It supports several different
> >> semantics of 'weak' references, including but not confined to those
> >> required by Java.
> >>
> >> If you can implement class unloading using those (which the current
> >> proposal does), then MMTk can help.
> >>
> >> If you want to put a pointer to the j.l.Class in the object header,
> MMTk
> >> will not care, as it has no way of knowing. If you put an additional
>
> >> pointer into the body of every object, then MMTk will see it as just
> >> another object to scan.
> >>
> >> Remember MMTk is a memory manager, not a Java VM!
> >>
> >>
> >> Conversely, supporting some exotic class unloading mechanism in MMTk
> >> shouldn't be hard and wouldn't deter me from trying it out.
> >
> >
> >
> > Robin, it would be great if you can get MMTk to support this class
> > unloading
> > effort. My main concern is the ongoing maintenance of MMTk class
> unloading
> > support.
>
> I haven't seen any proposal that requires MMTk to be modified, so it's a
> moot point at the moment.
>
> > A question for all involved. Is it possible to somehow make it appear
> that
> > the new objects related to unloading (VTable, ClassLoader, etc) are
> > always
> > reachable and thus never collected? I am trying to figure out a way
> to
> > make
> > integration of class unloading independent of correct support inside
> the GC
> > and JIT. This option could be a command line switch or compile time
> > option.
>
> Simple. Keep a list or table of these objects as part of the root set.
> Enumerate it optionally depending on a command line option.
>
> cheers,
> Robin
>
