Re: [xml] IO callbacks are not thread-safe

[Petr Pajas <pajas ufal mff cuni cz>]

On čt 2. dubna 2009, Daniel Veillard wrote:
> On Thu, Mar 26, 2009 at 07:06:14PM +0100, Nick Wellnhofer wrote:
> > The input and output callbacks of libxml are stored in static
> > arrays in xmlIO.c, so any use of the callback functions is not
> > thread-safe.
> >
> > In many cases this shouldn't be a problem, if callbacks are
> > registered only at the start of a program. But the Perl
> > bindings register and unregister callbacks every time a
> > document is parsed. I can reproduce
>
>   Uhhhh ????
> That sounds severely broken to me. Can you details why, and how ?
>
>
> > random segfaults or other errors when processing many thousand
> > documents in concurrent threads with the libxml Perl bindings.
> >
> > I'm willing to help fix this, but I'm not sure about the
> > correct approach. Should the callback arrays be added to the
> > global variables in globals.c?
>
> Those variables are not public, so I guess a different way would
> be preferable. Still I can't see any good valid reason to change
> the values all the time. Something is severely broken there in
> the perl bindings ! If they need a per parsing instance
> processing they should use the data block provided by the I/O to
> make the switch, but register an unified routine for all threads.
> No really this doesn't make any sense to me, but maybe you can
> come up with a valid reason,

Hi,

I think the original reason for this was that when Perl bindings are 
used with mod_perl, there may be other (non-Perl) components using 
the global callbacks differently; that's why XML::LibXML Perl 
module tries to clean after itself (restoring whatever was in the 
callbacks previously). Is there any other way around this?

-- Petr