crashes with python reference to destroyed objects (e.g exportToWkt() crashes when geom has been deleted)

[crschmidt]

When a feature is destroyed, if it has ownership over a geometry, it deletes that geometry. After that point, if one tries to call functions on the geometry, it will return nulls (Linux) or cause a KERN_PROTECTION_FAILURE (OS X).

This can be reproduced by selecting a feature, then typing the following into the Python console:

iface.activeLayer().selectedFeatures()[0].geometry().exportToWkt()

(Sometimes it requires calling it twice to reproduce the crash -- however, it will never return the correct answer.)

The reason for this appears to be that the feature created when it is pulled out of the list is then destoryed before exportToWkt() is called, taking the geometry with it.

A workaround is to instead call geometryAndOwnership(), which tells the feature to not destroy the geometry.

It seems like this problem may actually be exportGeosToWkb -- functions like wkbType() fail in the same way. It's possible that the mGeometry check at the beginning of these functions needs to move before teh exportGeosToWkb(), or that the exportGeosToWkb() needs to more resilient against being deleted.

[wonder]

The problem here is in python bindings because the scenario seems to be like this:

1. get feature
2. store geometry's reference in Python
3. feature is deleted (together with geometry)
4. reference in Python still exists, but the object it's pointing to doesn't

I'm trying to find out how to cope with this correctly...

Martin

[jef]

see also #1248

[lutra]

Hi,

what is the status of this issue?

cheers

[jef]

see also #2173

[pcav]

Still true?

[wonder]

This haven't been fixed yet

[brushtyler]

No crashes in my Ubuntu 9.04, but I never get the correct results.

I tried wkbType() on the same selected geometry a lot of times and I get different (and also strange) results: 0, 16777216, 7, 187101, 92, 143587, ...