bug#54458: 27.2; erc-dcc-get: Re-entering top level after C stack overflow

[Eli Zaretskii]

> From: Mattias Engdegård <mattiase@acm.org>
> Date: Tue, 29 Mar 2022 17:49:05 +0200
> Cc: Eli Zaretskii <eliz@gnu.org>, fernandodemorais.jf@gmail.com,
>         54458@debbugs.gnu.org, bandali@gnu.org
> 
> Although it seems reasonable to require that filter functions abstain from 
> sending more data to the process, there may be another way: preventing 
> re-entering process-send calls from recursing further.
> 
> Attached is a proof of concept: if process-send calls are invoked when 
> another activation already exists, just enqueue the data and let the previous 
> activation deal with the actual transmission. That nips the recursion in the 
> buds.
> 
> The principle seems sound but if anyone can think of problems with the 
> approach, please do tell.

I think this should be conditioned on the same process being used, no?
Doing this for two different processes doesn't cause problems, does
it?  If it does, can you describe in more detail how the recursion
happens?

Thanks.