Re: [Caml-list] Occasional malformed strings; OCaml -> OpenGL, via tgls/ctypes.

[Gabriel Scherer <gabriel.scherer@gmail.com>]

On Sun, May 8, 2016 at 5:04 PM, Jesper Louis Andersen
<jesper.louis.andersen@gmail.com> wrote:
> The problem there is too aggressive optimization on an ignore statement,
> but if the OpenGL bindings, or flambda is to blame is a bit up in the air to me.

If you look at the corresponding commit:

  https://github.com/LaurentMazare/tensorflow-ocaml/commit/111b4727cec992bab8bc67c22ccc8c31942ffbb2

It seems clear to me that the code was making un-portable assumptions
on the fact that using (ignore l) in a closure would force l to remain
live. It is not a bug of flambda if these kind of assumptions are
broken. (On the other hand, the fact that flambda breaks a lot of the
"probably too clever for its own good" code out there suggests that
one should be careful when adopting it.)

Note the nice trick to use the new 4.03 function opaque_identity in a
way that still works on older OCaml versions:

+ (* [opaque_identity] is not available pre 4.03, this hack ensure
that it + exists. *)
+ let opaque_identity x = x
+ let _ = opaque_identity
+ let opaque_identity = let open Sys in opaque_identity

On older versions, this is just a rebinding, on newer version this
uses "let open" shadowing.

(I suspect that the warnings that try to detect involuntary shadowing
may fire on this code, now or in the future.
Speaking of code slightly too clever for its own good...)

On Sun, May 8, 2016 at 5:04 PM, Jesper Louis Andersen
<jesper.louis.andersen@gmail.com> wrote:
>
> On Sun, May 8, 2016 at 7:08 PM, Anthony Tavener <anthony.tavener@gmail.com>
> wrote:
>>
>> TL;DR: Constant string like "fontColor" can (rarely) come out like
>> "\220\552\663\1" after foreign call to OpenGL.
>
>
> It may be flambda-related, as the following problem looks much like it:
>
> https://github.com/LaurentMazare/tensorflow-ocaml/issues/7
>
> I hit that last week with flambda. The problem there is too aggressive
> optimization on an ignore statement, but if the OpenGL bindings, or flambda
> is to blame is a bit up in the air to me.
>
>
> --
> J.