Crash of python when exiting the interface ("python: double free or corruption")

[francois-keith]

Hello all,

Since the merge #4, there is a problem at the destruction of the python interface used to interact with the SoT in some cases.

To reproduce the error, create the file test.py with the following content:

from dynamic_graph.sot.core.matrix_util import matrixToTuple
from dynamic_graph.sot.dynamics.angle_estimator  import AngleEstimator

Running python ./test.py
Returns the following error:

*** glibc detected *** python: double free or corruption (fasttop): 0x00000000028b5870 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x7eb96)[0x7f964559db96]
/usr/lib/x86_64-linux-gnu/libstdc++.so.6(_ZNSsD1Ev+0x1f)[0x7f96433f751f]
/lib/x86_64-linux-gnu/libc.so.6(+0x3b901)[0x7f964555a901]
/lib/x86_64-linux-gnu/libc.so.6(+0x3b985)[0x7f964555a985]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf4)[0x7f9645540774]
python[0x41bb31]
======= Memory map: ========
00400000-00670000 r-xp 00000000 08:06 4066903                            /usr/bin/python2.7
00870000-00871000 r--p 00270000 08:06 4066903                            /usr/bin/python2.7
00871000-008da000 rw-p 00271000 08:06 4066903                            /usr/bin/python2.7
008da000-008ec000 rw-p 00000000 00:00 0 
00951000-0100d000 rw-p 00000000 00:00 0                                  [heap]
...
(then there is the list of loaded libraries.)

This crash occurs because the library libsot-dynamic.so is loaded after the library libsot-core.so.
At the opposite, the following code will properly exit:

from dynamic_graph.sot.dynamics.angle_estimator  import AngleEstimator
from dynamic_graph.sot.core.matrix_util import matrixToTuple

Note that this is only due to the fact that in dynamic_graph/sot/dynamics/__init__.py, the Dynamic entity is the first one loaded. With this

from angle_estimator import AngleEstimator
from dynamic import Dynamic

the test would also crash.

Is there a way to correct this?
For now, I have to use a workaround that consists in systematically importing

from dynamic_graph.sot.dynamics.dynamic import Dynamic

first, so as to avoid this issue.

[florent-lamiraux]

Hello François,

Some of us noticed the issue. I tried to track the error with valgrind but without success. According to valgrind, there is a double free error in the destructor of std::string, but I have been unable to find which string is the source of the problem. Your experimentation above is another interesting clue. Mehdi suggested to compile python with -g flag and to reproduce the error in gdb.

We need to investigate further.

Florent