Re: [Xen-devel] [PATCH 16/28] libxl: ocaml: use the "string option" type for IDL strings

[Rob Hoes <Rob.Hoes@xxxxxxxxxx>]

[...]
> > +           CAMLreturn(Val_some(caml_copy_string(c_val)));
> 
> A bad sequence is:
> 
>    1. caml_copy_string() allocates a string successfully
>    2. Val_some() calls the allocator to allocate a block but the minor heap is
> full so it triggers a GC
>    3. the GC deletes the string from (1) since it can't find any references 
> to it
> 
> Personally I always force myself to write very basic code with lots of 
> explicit
> temporaries, just to be totally safe. It feels strange because it's the
> complete opposite of good functional style (particularly if you believe in
> point-free programming!).
> 
> So I would write:
> 
>    CAMLparam0()
>    CAMLlocal2(tmp1, tmp2)
>    if (c_val) {
>      tmp1 = caml_copy_string(c_val);
>      tmp2 = Val_some(tmp1);
>      CAMLreturn(tmp2)
>    }
>    ...
> 
> It's almost embarrassing to write code like that, but at least it's safe! :-)
[...]

Agreed!

Cheers,
Rob

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