fixed segfault on shutdown

[rhaschke]

rviz always crashed on shutdown with MotionPlanning display loaded.
Reason was, that Kinematics pointers were destroyed after the underlying library was unloaded.

Use of pluginlib's createUnmanagedInstance() is strongly discouraged:
http://wiki.ros.org/class_loader#Understanding_Loading_and_Unloading

There are several other locations in the source, where the discouraged createUnmanagedInstance() is used!

[rhaschke]

The patch actually replaces the inconspicuous segfault message with a shiny warning message from class_loader, that the order of pointer releases is wrong - which was exactly the reason for the segfault.

Digging a little bit deeper, I found the underlying reason:
The SharedStorage maintains a static storage of RobotModelLoaders, which gets freed only very late in the stutdown process. On the other hand, the PlanningSceneMonitor directly allocates a RobotModelLoader first. When releasing this RobotModelLoader at destruction time of the PlanningSceneMonitor, the kinematics plugin lib will be unloaded too.
I guess, that's an issue in the class_loader lib, which should be aware of several independent resources accessing the same lib.

[rhaschke]

Digging even further, I believe, that MultiLibraryClassLoader must not unload all libraries in its destructor without checking usage counts.

[davetcoleman]

Wow, I'm impressed you dug that deep and found this. I believe I've occasionally seen this issue, too. I haven't tested it but it seems like a good merge, +1

[sachinchitta]

I tried this a bunch (with the jade source branches though) running demo.launch and killing it. Rviz does not crash for me always - in fact very rarely. I do think this is a good fix but is there a demo.launch you are using that is always making this happen?

[sachinchitta]

Ok - seemed to be happening in indigo but not in jade.