Re: [Caml-list] Accelerating compilation

[Wojciech Meyer <wojciech.meyer@gmail.com>]

Xavier Leroy <Xavier.Leroy@inria.fr> writes:

>> 3) Parallel compilation in Ocamlbuild
>> Of course it would help but it is not easy to implement so I'm just
>> putting it there to be exhaustive.
>
> As others said, ocamlbuild has some support for parallelism, but
> it's much less effective than "make -j".  One reason could be that
> ocamlbuild discovers dependencies as it goes, so it's doing online
> scheduling, in contrast with make's offline scheduling.  But within
> the online scheduling approach, there is certainly room for
> improvement.  Suggestions and patches welcome.

That's exactly what happens and is described here:

  http://caml.inria.fr/mantis/view.php?id=5754

Unfortunately it's not that easy to fix. Possible solutions:

- do the scheduling after the project was build for the first time and
  then:
  * for each of the targets note the products and store it in the
    database
  * when the target changes, re-build the database for this target and
    it's products

- provide simpler and less dynamic rules for ocamlbuild:
  * that actually don't run the Caml code, but do only invoke shell
    commands with some substitution
  * try to convert existing rules to the static ones

Both solutions guarantee perfect scheduling.

Wojciech