Re: BDW-GC branch updated

[Andreas Rottmann <a.rottmann@gmx.at>]

ludo@gnu.org (Ludovic Courtès) writes:

> Andreas Rottmann <a.rottmann@gmx.at> writes:
>
>> Will going from a precise GC to BDW-GC not have drawbacks? IIRC, the PLT
>> people went in the opposite direction. A quick google turned up this:
>>
>> http://www.cs.brown.edu/pipermail/plt-scheme/2006-June/013840.html
>>
>> I wonder if the reasons for switching to a precise GC listed in there
>> will also apply to Guile.
>
> Thanks for the link!
>
> They write:
>
>   There is one known problem, though, related to linked lists [Boehm,
>   POPL'02].  Unfortunately, we seem to hit this problem often in
>   practice, due to the way that threads and continuations are
>   implemented, and there doesn't seem to be a reliable way around it.
>
> The paper is "Bounding Space Usage of Conservative Garbage Collectors",
> available from http://www.hpl.hp.com/personal/Hans_Boehm/gc/ .  It
> depicts scenarios where "false references" lead to unbounded data
> retention.  My interpretation of these scenarios and the "Summary"
> section is that these cases are hopefully quite rare.
>
> Now, I don't have enough experience of long-running BDW-GC applications
> to know whether it's a problem in practice.  The PLT folks surely had
> more experience (but with a different implementation IIUC).  There are
> also other schemes that use BDW-GC, such as Bigloo.
>
> However, it doesn't worry me as much as the current GC bugs (e.g., [0, 1]).
>
> Also, there are definite benefits to using a conservative GC for
> libguile, given how tightly it can be integrated with C (e.g., [2]).
>
My main concern is/was that by moving to a conservatice GC, and
_consequently changing the API of libguile to assume a conservative GC_
(as outlined in [2]), you get third code relying on that as well. This
would make it effectively impossible to ever switch back to a precise GC
without potentially breaking all third-party code using the libguile
API.

However, take that just as my < 2€-cent ;-).

Regards, Rotty
-- 
Andreas Rottmann -- <http://rotty.yi.org/>