[fpc-devel] Improving Ref Counting

[Jamie McCracken]

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)

>  
> 
>>>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.

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.


> 
> 
>>>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.

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

Multithreaded environments too?


jamie.


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