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Re: Implementation details of VMStackWalker
From: |
Andrew Haley |
Subject: |
Re: Implementation details of VMStackWalker |
Date: |
Sun, 24 Jul 2005 10:38:20 +0100 |
Mark Wielaard writes:
>
> On Fri, 2005-07-22 at 18:01 +0100, Andrew Haley wrote:
> > Ingo Prötel writes:
> >
> > > I just implemented VMStackWalker for our VM and have some questions.
> > >
> > > The reference implementation of 'getCallingClass()' and
> > > 'getCallingClassLoader()' just look at the third entry in the class
> > > context. Would it not be better to return the first class that is not
> > > assignable to the class in context[0] ? That way we could cope with
> > > classes that first call some private or protected classes an then ends
> > > up calling the stack walker.
> >
> > In gcj, we have a method called GetCallingClass(Class c). It searches
> > firstly for a method declared in class c, then for a method not
> > declared in c. We have found, after a certain amount of trouble, that
> > this is the right way to do things; it means that an arbitrary number
> > of stack frames can be between the direct caller of GetCallingClass
> > and the user code, and it also means that you don't have to check for
> > assignability, but for an exact match.
>
> I proposed something similar a while ago:
> http://lists.gnu.org/archive/html/classpath-patches/2005-01/msg00138.html
>
> Jeroen did object strongly to this approach though since he felt that
> having (and constructing) an extra argument for this function was too
> much overhead for runtimes that didn't need it to begin with.
Well, that's up to the VM implementer. IMO trying to unify low-level
stack walker code is unnecessary and leads to too many compromises;
it's a merge too far.
However, as for overhead -- I don't believe it. I doubt that not
having this parameter saves anything much on any VM.
Andrew.