[lxml-dev] Proxy AssertionError in threaded tree traversal

[Holger Joukl]

Hi,

Stefan Behnel <stefan_ml at behnel.de> schrieb am 10.02.2007 22:14:32:

> Stefan Behnel wrote:
> > What you observe is definitely a threading issue. The code in
> _elementFactory
> > (etree.pyx) suggests that different threads are concurrently
> creating proxies
> > for the same node.
>
> Rethinking this, I'm now wondering how this should be possible. The
function
> uses Python code, so we are always sure it is protected by the GIL when
it is
> called (otherwise we'd get a Python crash), so there /is/ no concurrency
here.

Is the compiled-to-C _registerProxy function an atomic operation regarding
GIL-
locking? Because inside it uses Python-API calls itself, wouldn't that mean
there
can be a thread change when in the function?

> Could you try to come up with a (preferably short) list of things that
your
> threads are doing concurrently? Knowing which parts of the API are used
should
> make it easier to see where the problem might arise.

I'm currently failing to put together some sort of minimal example but I've
just seen the AssertionError in code where I actually _do_ deepcopy the
element
before the worker thread does anything on it.
We are currently trying to track down severe segfault/bus error problems
and
right now I'm still unsure which of the components is responsible for them.
But I'm beginning to think that the AssertionError is merely another
symptom
of this, meaning that c_node._private has been corrupted by the villain,
whoever it is.
I'm now trying to strip down my test programs and will probably try to
recompile with
different libxml2/libxslt versions.

Holger

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