Re: [Caml-list] local root registration

[Markus Mottl <markus@oefai.at>]

On Fri, 22 Feb 2002, Winfried Dreckmann wrote:
> I agree that they are easiest if one strictly follows the rules in the
> documentation. However, I would like to point out that there are cases
> where one does not want to do this. In these cases, the older macros
> (Begin_roots and End_roots) are much more flexible, and can even lead
> to better code.

Yes, to me they also seem more approriate at times.

> I will discuss this a little. Perhaps the Begin_roots/End_roots macros
> should not be deprecated, but left as a low level alternative?

I can't remember that there were intentions to remove them. They rather
seem to be discouraged in favour of the new scheme whenever the latter
can be applied without tradeoffs.

> In one case the documentation already differs between a simple and a
> low level interface, and I believe this is a good approach. What do
> other list members think?

There should certainly be an efficient way to conditionally protect
roots, which cannot be done with the new macro scheme. Furthermore,
to my knowledge there is currently no way to allocate and raise more
complex exceptions with "mlraise" without using the older macros.

> (see "lib/common/ml-alloc.h" in the numerix distribution). In this way,
> the price for garbage collection is only paid if allocation actually
> takes place. It seems impossible to achieve the same effect with
> CAMLxxx macros.

If I am not seriously mistaken, only allocations on the OCaml-heap can
trigger a collection. There is just a small overhead associated with
(un)registering OCaml-values as reachable, but it's certainly a good idea
to remove every kind of unnecessary overhead in performance-critical code.

Regards,
Markus Mottl

-- 
Markus Mottl                                             markus@oefai.at
Austrian Research Institute
for Artificial Intelligence                  http://www.oefai.at/~markus
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