Re: [Pyode-user] Segfault Due to Gcmodule Error

[Chris B. <chr...@gm...>]

On 15/06/07, Chris Spencer <chr...@gm...> wrote:
> I'm using PyODE with Cherrypy, and whenever the server's autoreload
> feature runs, Python segfaults with the error:
>
> python: Modules/gcmodule.c:276: visit_decref: Assertion
> `gc->gc.gc_refs != 0' failed.
>
> However, Python only segfaults if I've imported ode in any of my
> Cherrypy scripts.
>
> Based on discussions of similar problems, the cause is likely a bug in
> ODE's C code generated by Pyrex. I wouldn't know where to begin
> debugging such a problem. Could anyone offer suggestions?

The problem is that the destructor order is essentially random when gc
is used. ODE (not pyode) doesn't have any ownership rules for objects,
and objects point to each other, so deallocating objects causes memory
protection faults. This is also a problem with C++ ODE code, python
with gc just aggravates the problem. In my Simulator.__del__ function
I have something like:

        for j in self.joints:
            j.attach(None, None)
        for g in self.space:
            if g.placeable():
                g.setBody(None)
        # destroy hanging geoms
        ode._geom_c2py_lut.clear()
        del self.joints
        del self.space
        del self.geoms
        for bg in self.bpgs:
            bg.destroy()

As you can see, I have to manually remove links between objects, and
then destroy them all n a particular order. I don't use gc.

You can see the memory errors by running valgrind, it will generate
loads of warnings; use suppression files,
http://svn.python.org/projects/python/trunk/Misc/valgrind-python.supp
and opengl.supp from
http://www.openscenegraph.com/index.php?page=Documentation.TipsAndTricks

There's a bug report for ODE at
https://sourceforge.net/tracker/?func=detail&atid=382799&aid=1566350&group_id=24884