@pinned classes

[Justin Spahr-Summers]

On Thu, 01 Apr 2010 18:58:47 +0100, div0 <div0 at users.sourceforge.net> 
wrote:
> 
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> Justin Spahr-Summers wrote:
> > On Wed, 31 Mar 2010 22:59:08 -0400, bearophile 
> >>
> >> Bye,
> >> bearophile
> > 
> > I think the D2 spec puts restrictions on what you can do with GC-
> > allocated pointers (can't convert them to integers, can't perform 
> > arithmetic on them outside of their bounds, etc.), and I think they're 
> > restrictive enough that a copying garbage collector could work with no 
> > changes to compliant code.
> > 
> > - Justin Spahr-Summers
> 
> The trouble with a moving garbage collector is that you have to be able
> to accurately scan the stacks of all threads. This is difficult to do
> with a language that can arbitrarily call into functions provided by
> different languages for which the compiler won't and can't have stack
> layout info.
> 
> It's especially a pain on windows, as D code is called from window
> procedures, so most code is already using a stack which can't be scanned.
> 
> Might be more doable on linux, xlib has a vastly better design than win32.
> 
> - --
> My enormous talent is exceeded only by my outrageous laziness.
> http://www.ssTk.co.uk
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My knowledge of garbage collection techniques isn't as extensive as I'd 
like it to be. My previous reply was mostly an assertion that the D spec 
is strict enough about GC-managed pointers that more advanced/precise 
garbage collectors SHOULD theoretically be possible, although there may 
be platform-imposed obstacles like what you mentioned.

For instance, I think the standard is specific enough that maybe GC-
managed "pointers" could be implemented as indices into a managed-memory 
lookup table, using an actual pointer when calling extern (C) functions 
or some such. I really doubt this is an optimal implementation, but my 
understanding is that it should be possible without any code changes to 
compliant D programs.