[Gluster-devel] glusterd crashes when synctask is used in conjunction with inner functions.

[Jeff Darcy]

On October 8, 2012 7:02:34 AM Krishnan Parthasarathi 
<kparthas at redhat.com> wrote:
> I have been rewriting some of the volume operations (like volume-start,
> volume-add-brick, volume-remove-brick) using synctask library (aka syncops).
> This change has the following immediate benefits,
>
> - volume-start would return success/failure depending on the success/failure of
>   brick process(es) spawned.
> - would make glusterd's epoll thread 'more' available.
>
> </context>
>
> While I was making the changes in http://review.gluster.com/3969, I 
> noticed that
> whenever the code executing on a synctask called into dict_foreach, 
> which was supplied
> a function ptr, defined as an inner function, glusterd crashed. When I rewrote
> inner function as a static function, glusterd wouldn't crash.
>
> Has anyone seen or can explain (or give possible leads to analyse) this 
> behaviour?
> FWIW, inner functions are only available as part of GNU extensions to C. So, I
> assumed it is not such a bad thing to move the inner functions 'out', 
> in my patch.

Ugh.  I noticed this pattern while I was looking at some AFR stuff 
recently.  I thought it was rather clever, and pondered a bit about how 
it might be implemented in gcc/libc.  Apparently it was a bit too 
clever, and the implementation leaves something to be desired.  An 
inner function might be more elegant than defining private structures 
to pass through our own context pointer, but in the interest of both 
portability and not having to debug compiler code I think changing 
these to work the "old fashioned" way would actually be a good thing.