Re: [Fresco-devel] Graphic_var's and server stability

Stefan Seefeld wrote:
> Neil Pilgrim wrote:
[...]
> > - an unreleasable reference leads to the Graphic in the server (ie.
> > vfill) not being unallocated when it is no longer required, since there
> > will always be one client-side reference.
> 
> that's not true in general. It is true if you use distributed ref counting
> (as we do), where the lifetime of proxies is coupled to the lifetime of
> servants (using the right smart pointers, of course).

OK, I was getting worried that I had half the idea wrong until this
point.

Thanks for the analysis; I already understood the first part, ie. that
you should always release Foo_ptr's returned from corba calls, but
didn't think (doh) about how it would fit into 'nested' calls.

> > Is this a correct analysis? If so I think it would be useful, in
> > addition to a coding style-guide, to have a 'corba style guide' or
> > similar, maybe in a FAQ style, with gotchas like the above. Perhaps I've
> > just not read H&V cover-to-cover enough, but although a problem like
> > this is hinted-at, its not made explicit?
> 
> I totally agree, this whole issue can't be stressed enough. I'v started
> to cover it in the tutorial at http://www2.fresco.org/tutorial/index.html
> (Appendix B), and everybody is welcome to comment on that (and even enhance
> it !)

For some reason I thought of the tutorial as an architectural
introduction, but of course its a programming one too :) BTW, we'll need
an update as and when resolve_server is used wrt the nameserver not
being mandatory, etc. Maybe it might be worth having somewhere to list
extra parts to the tutorial that need adding, like this? A task perhaps?
(we could use the wiki, but a task gives more of a way to say when we're
completed, which would be useful IMO)

TBH something like this is maybe more important than just an appendix:
to introduce people to programming in fresco, we need to teach them
corba first, without putting them off too much. Then again, people
should read *all* the docs ;)

> > If I got the above correct, what I'm also concerned with is the way that
> > a client could easily be (badly) written such that it leaks
> > graphic-references. When this client exits, will all the graphics that
> > it requested be deleted? I believe that would be desirable; even if we
> > want to keep some graphics from the client, they could be copied before
> > the client quit, but I'm not sure if this would remove the benefits of
> > deleting the original graphics.
> 
> yes, all resources allocated by the client will be released when the client
> disconnects, no matter how. That's indeed crucial.

Doh! Yes, of course, I knew that this was the case, but didn't associate
it with the leaking-reference problem! POA's are good :)

Thanks Stefan,

-- 
Neil