[fpc-devel] Improving Ref Counting

[Marco van de Voort]

> > a valid/invalid reference without accessing memory that is invalid in the mean
> > time.
> 
> How does a GC do this? It would have the same problem?

A GC manages all memory, local variable allocation inclusive. IOW, the
way a GC does it, is not possible in a mixed environment.
 
> > Also note that the list of references must be a dynamically size structure,
> > incurring getmem and size-change overhead on a simple assignment.
> 
> yes a "single linked list" is a very efficient dynamically sized 
> structure and much cheaper than try..finally or using Tlist.

It's very expensive. getmem is quite expensive, and you need it for every
reference this way.

> > I doubt performance would improve, specially since the edge of this problem
> > (the worst 90%) can be taken off by simply disabling try...finally generation
> > in places where they are unlikely to happen.
> 
> Is there a real failsafe way of doing that?

Nothing is failsafe. However e.g. in RTL string routines exceptions
shouldn't occur unless memory is exhausted, in case it doesn't matter
much anyway.