[fpc-devel] Improving Ref Counting

[Marco van de Voort]

> Marco van de Voort wrote:
> >>>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.
> 
> Are you saying it would be a managed pointer then which is allocated on 
> the heap? (I had assumed the pointer would be on the stack and the 
> object in the heap)

That is a solution yes. Or on the stack, but on termination the reference
is killed, and you are back at the try..finally again

> > It's very expensive. getmem is quite expensive, and you need it for every
> > reference this way.
> 
> Okay then use Tlist with preallocation of say half a dozen references - 
> that should be efficient for 99% of cases for an individual object's 
> references.

Still an dyn allocation extra. Ansistring performance is partially bound
to it, and you double it.

> > 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.
> 
> What about all other non string exceptions that can occur between 
> creation and destruction of the ansistring?

They lead to mem leaks.
 
> Multithreaded environments too?

Yes.