Re: [MirageOS-devel] mirage-logs and functoria

[Thomas Leonard <talex5@xxxxxxxxx>]

On 12 January 2016 at 14:00, Drup <drupyog+caml@xxxxxxxx> wrote:
>> Ideally, I'd like to integrate this with functoria. What would be the
>> best way to do this?
>> Is it possible to do something like this?
>>
>>    register "console" [mirage_logs (main $ default_console)]
>
>
> Not directly like that. I see several possibilities.
>
> - Make "Main" take an extra module argument
>       module L = struct let log = create () |> run end
>   then config.ml is now
>       let log = default_log $ default_console in
>       register "foo" [main $ .. $ log]
>
>   This way, the functor application of Mirage_logs.Make is outside (in the
> "default_log" combinator).
>   Maybe it could be combined with Logs.Src.create if that's desirable.
>
> - Change a bit the API, so that you have a `start` function that returns a
> thread that starts the logger
>   (which means no automated function wrapping).
>
>   Then, we declare main differently:
>        let main = foreign ~deps:[hidden default_log] "Unikernel.Main" ( ...
> @-> job)
>   `Main.start` will receive an additional value (at least unit, but you can
> put whatever you want).
>   and that ensures that logs are initialized before the main job is
> executed.
>   This is what is done for nocrypto.

Do you mean "before the main job's start function is called" or
"before any of the inputs are evaluated"? The second would be OK. The
docs say:

    {- If [deps] is set, the given list of {{!abstract_impl}abstract}
       implementations is added as data-dependencies: they will be
       initialized before calling [name.connect]. }

However, there is no [name.connect] function. If it means [name.start]
then I don't see what the difference is between this and declaring it
as a regular argument.

>   Function wrapping could probably be arranged by using the value passed
> around.
>   In the end, this could be like 1), but without the functor argument.
>
> - The problem with those two methods is similar to your tracing issue. It
> doesn't log things started before the main job.
>   The third possibility is, we solve
> https://github.com/mirage/functoria/issues/45 and we add a way to put the
> logger (and the tracer) there.
>   Again, no automated wrapping

Yes. I think we have a slight advantage here: libraries using Logs
will be written to assume that there will be no log output until their
connect function is called (whereas libraries aren't generally aware
that they might be being traced). However, being able to trace the
connect calls is really useful, so waiting until Main.start is too
late.


-- 
Dr Thomas Leonard        http://roscidus.com/blog/
GPG: DA98 25AE CAD0 8975 7CDA  BD8E 0713 3F96 CA74 D8BA

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