parrot-dev Digest, Vol 48, Issue 6

[Bart Wiegmans]

Hi everybody,

Let me elaborate on the e-mail I sent before. First, two test cases to
prove the problem is not imaginary (boy, that would suck :-)). For
this I've created a github repo:

https://github.com/bdw/multiple-interpreters.git

With the latest push on my find-root-interpreter branch,
child_interpreters runs until interpreter destruction, upon which it
crashes. I don't really know why (although it happens in main_arena,
but there seem to be no debugging symbols in that function on my local
install).

What bothers me a bit is that I don't really know how this should be
done and dealt with.

Kind regards,
Bart Wiegmans

> Date: Sun, 5 Aug 2012 11:27:12 +0200
> From: Bart Wiegmans <bartwiegmans at gmail.com>
> To: parrot-dev at lists.parrot.org
> Subject: Interpreter scheduler and Child interpreters
> Message-ID:
>         <CADc7B-+L9zCKJMfVn1F=ikaANKmZu3ER3y6akZK4aUVj-NmULA at mail.gmail.com>
> Content-Type: text/plain; charset=UTF-8
>
> Hi everybody!
>
> Once again, working on mod_parrot, I noticed a bit of an issue with
> parrot. But I can't really get to how to resolve it, so I'm asking
> your advice.
>
> The context: I want to run multiple interpreters in the same program,
> at the same time, running different programs. This is a requirement
> because otherwise, mod_parrot can only run in the prefork apache mpm,
> which uses a relatively large amount of memory and other resources and
> for this reason is not very popular with web hosters. Thus, without
> running in a multi-threaded enviroment, mod_parrot is nearly useless.
>
> This is not as simple as it seems, because of the following:
> * having two separate interpreters at the same time is apparantly not
> very ok, unless they are parent and child (no idea why)
> * but if a child is instantiated it does not get a scheduler of its
> own (Parrot_cx_init_scheduler)
> * which causes it to crash when starting execution because
> interp->scheduler is 0x0 (literally everywhere in src/scheduler.c)
>
> Thus, I created a new function in src/interp/api.c, called
> Parrot_interp_get_scheduler, and combed through the code to replace
> direct access of the scheduler with this delegated access. However,
> considering the amount of places that it was directly accessed, and
> seeing the behavior of it, I'm actually doubting whether it is a good
> idea. I in fact doubt whether having multiple interpreters is a good
> idea at all given the current state of things. For this reason I'm not
> placing a pull request right now, but I do ask you to review the
> changes in the branch, please see
> https://github.com/bdw/parrot/tree/find-root-scheduler .
>
> Kind regards,
> Bart Wiegmans
>
>
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> End of parrot-dev Digest, Vol 48, Issue 6
> *****************************************