Re: Exceptions (was Re: Custom extensions to Lua)

[Lisa Parratt <lisa@...>]

On 12 Aug 2005, at 15:42, David Given wrote:
> Hmm. It has possiblities. Thinking off the top of my head, some  
> questions that
> come to mind are: What about function calls?

Because the finalised object is stored at the lua_State level, it  
should survive function calls. Only thing to prevent is garbage  
collection from happening in the middle of garbage collection,  
assuming this hasn't already been prevented.

> Would doing this still allow you
> to pass the finalised object in as a parameter?

Hmm - actually, I'm wrong - wrong op codes.

I believe load and move only apply to locals, intermediates and  
function calling conventions? All of these should be ok - these can  
only effect their own scope and below. What must be prevented are up  
value accesses (their own opcode, iirc?) and global accesses, done  
through preventing table sets, which also prevents a local table  
reference from leaking a reference.


> What about constructing a
> table containing the object and then saving the table?

The above should prevent the finalised object from being made a table  
member. :)

> but it *does* mean that objects may have their finalisers
> called multiple times.

Surely the postamble to the code that calls the finaliser could  
disarm the finaliser, preventing multiple fires?

> The garbage collected also has to be more complex,
> because when you resurrect an object to put into the table, you  
> need to make
> sure that none of its members have been collected.

Surely it doesn't get resurrected? The GC is doing the collect, so  
once it reaches this object, it can put it into the table. Prior to  
that instant it wasn't aware the object was redundant. Therefore, all  
of it's children will still consider it a valid reference, and so  
can't have been collected prior to this point.  Since the GC doesn't  
collect it, but puts it in the table, it remains a valid reference,  
so the children don't get collected after that point.

--
Lisa
Really should sort my sig out