Re: [Caml-list] segfault in simple program with 4.02 native

[Martin Jambon <martin.jambon@ens-lyon.org>]

On 09/13/2014 03:26 AM, Martin Jambon wrote:
> On Sun 07 Sep 2014 06:28:34 PM PDT, Martin Jambon wrote:
>> On Sun 07 Sep 2014 11:47:43 AM PDT, Alain Frisch wrote:
>>> On 9/6/2014 7:51 AM, Martin Jambon wrote:
>>>> Thanks for the explanation, Jeremy. I guess atdgen will have to use
>>>> "option refs" after all unless someone has a better idea.
>>>
>>> I might be missing some context, but the current code seems to playing
>>> two different tricks with the type system:  using (Obj.magic 0.) as a
>>> dummy initial default value (to avoid references) and mutating
>>> normally immutable fields with Obj.set_field.  Is that right?
>>
>> Yes, exactly.
>>
>>>  You
>>> might be able to keep the first trick, but storing the values in local
>>> references instead of field of the the target record (if those
>>> references don't espace from the function, they will be represented as
>>> local mutable variables, whose mutation might actually be more
>>> efficient than those of the record fields),  building the target
>>> record at the end by reading from those references.
>>
>> Christophe Troestler also suggested this solution in a private reply.
>> I was afraid of the cost of the refs, so it's great to know that
>> they're optimized away.
>
> I think we now have a working implementation for json readers in atdgen
> (https://github.com/mjambon/atdgen/tree/fix-magic-ocaml402).
>
> However, atdgen also supports a binary format called biniou (Intro:
> http://mjambon.com/biniou.html Spec:
> https://github.com/mjambon/biniou/blob/master/biniou-format.txt). It is
> broken for the same reason as the JSON readers, but it is trickier to
> fix. Biniou allows sharing records and cyclic data. So far readers have
> been working by first creating a record with uninitialized fields, and
> then by proceeding with reading the field values. If a reference to the
> record is found, we just use the record that we already created, even if
> some of its fields are still unset.
>
> The problem here is that we need to create the record before reading its
> fields. Perhaps we could use the solution proposed by Milan Stanojević
> earlier in this thread, consisting in creating a private record type
> with mutable fields and at the end convert it to the normal type using
> Obj.magic.
>
> ... Or we could just drop support for some features, hence the following
> questions:
>
> 1. Does anyone use biniou at all?
> 2. Does anyone use biniou with cyclic data?

atdgen 1.4.0 is out (soon in opam). It should work with OCaml 4.02 for 
both json and biniou.

I dropped support for sharing, so no more support for serialization of 
cyclic data using biniou.


Martin