Re: [Chicken-users] Stack space allocation

[felix]

John Lenz wrote:
> Well, after a bunch of searching, I found this
> http://www.gnu.org/software/libc/manual/html_node/GNU-C-Variable-Size-Arrays.html 
>
>
> which seems to imply that alloca persists until the function returns,  
> unlike arrays which last until the end of the block.  The man page for  
> alloca also states that the memory persists until the end of the  
> function call.  So I will write the SWIG interface functions to assume  
> that alloca will always be unique.

Fine.

> > 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?
>
>
> Well, this is for the SWIG wrapper, so the list will be as long as  
> whoever is using SWIG inputs.  Ideally, we would not like to place  
> restrictions on the size, so that SWIG will work for whatever purpose.   

Agreed.

> Is there a better way to allocate data space?  alloca works for things  
> like return values and a few paramaters, but for very long lists, it is  
> probably a bad idea to stick all that allocation on the stack.  (maybe  
> it is a good idea...?)

You can use C_alloc_in_heap(). But the cleanest solution is to mimick the
way compiled code allocates it's "literal frame":

- use C_demand2() to check whether there is enough space on the heap
- if there isn't enough space, invoke "C_rereclaim2(<needed storage>, 1);"
- if there is, invoke C_pair() (and friends) with the allocation pointer
  C_heaptop (like: "mypair = C_pair(C_heaptop, car, cdr);")


cheers,
felix