Re: [Chicken-users] Stack space allocation

[felix]

John Lenz wrote:
> Hi.  I am in the process of redoing the swig stuff, and I have a  
> question about C_alloc.
>
> Would the following code be valid?

[...]

> What I am concerned about is alloca calls inside a C block.  I am  
> unsure if the compiler might be optimizing stack space.  That is, since  
> I create three blocks, it would assume that stack space can be shared  
> between them and then the alloca call would return the same space to  
> all three blocks.

Yes, I agree that this might be dangerous. It's preferable to alloc all
the storage at once. C_pair will update the known_space pointer
accordingly on every initialization.

> Also, when wrapping say a std::list I would like to do something like
> for (i = list.begin(); i != list.end(); ++i) {
>  C_word *space = C_alloc(C_SIZEOF_PAIR + C_SIZEOF_SWIG_POINTER);
>  C_pair(...);
> }
> would that also be acceptable?  The compiler won't optimize the stack  
> space usage so that every iteration has new data space.
>
> or would say
> C_word *space = C_alloc((C_SIZEOF_PAIR + C_SIZEOF_SWIG_POINTER) * list. 
> size());
> and allocate it all at once work better?
> Note the list.size() is a O(n) operation.

It usually is (even though it doesn't _have_ to be). If you can be sure that
the compiler wont optimize things away (and I don't know right now), then
the former approach might be ok.
Are the lists potentially very long?


cheers,
felix