consistent signal 11 during application close

[anupamk]

hi,

i am seeing the following crash (consistently) during Py_Finalize. here is the back-trace

 gdb ./basic
GNU gdb (GDB) 7.11.1
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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Reading symbols from ./basic...(no debugging symbols found)...done.
(gdb) run
Starting program: /home/anupam/source-code/c++/matplotlib-cpp.git/examples/basic 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".

Program received signal SIGSEGV, Segmentation fault.
0x00007fffe94fd1d3 in QApplication::~QApplication() () from /usr/lib/libQtGui.so.4
(gdb) where
#0  0x00007fffe94fd1d3 in QApplication::~QApplication() () from /usr/lib/libQtGui.so.4
#1  0x00007fffea5927a9 in ?? () from /usr/lib/python2.7/site-packages/PyQt4/QtGui.so
#2  0x00007fffea5928ce in ?? () from /usr/lib/python2.7/site-packages/PyQt4/QtGui.so
#3  0x00007fffeb8f4c89 in ?? () from /usr/lib/python2.7/site-packages/sip.so
#4  0x00007fffeb8f62a9 in ?? () from /usr/lib/python2.7/site-packages/sip.so
#5  0x00007ffff7a92c53 in subtype_dealloc () from /usr/lib/libpython2.7.so.1.0
#6  0x00007ffff7a747df in insertdict_by_entry () from /usr/lib/libpython2.7.so.1.0
#7  0x00007ffff7a76330 in dict_set_item_by_hash_or_entry () from /usr/lib/libpython2.7.so.1.0
#8  0x00007ffff7a7b1ec in _PyModule_Clear () from /usr/lib/libpython2.7.so.1.0
#9  0x00007ffff7aeed5d in PyImport_Cleanup () from /usr/lib/libpython2.7.so.1.0
#10 0x00007ffff7afb0fd in Py_Finalize () from /usr/lib/libpython2.7.so.1.0
#11 0x0000000000402201 in matplotlibcpp::detail::_interpreter::~_interpreter() ()
#12 0x00007ffff6de5990 in __run_exit_handlers () from /usr/lib/libc.so.6
#13 0x00007ffff6de59ea in exit () from /usr/lib/libc.so.6
#14 0x00007ffff6dd0298 in __libc_start_main () from /usr/lib/libc.so.6
#15 0x000000000040143a in _start ()
(gdb) 

'basic' here is examples/basic.cpp

here are some environment details:

g++ --version
g++ (GCC) 6.2.1 20160830
Copyright (C) 2016 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

uname -a
Linux fatcat 4.7.4-1-ARCH #1 SMP PREEMPT Thu Sep 15 15:24:29 CEST 2016 x86_64 GNU/Linux

of course, removing the Py_Finalize from the destructor 'solves' the problem, but that is cheating :)

[lava]

Hm, interesting :) To be sure, this is on an unmodified examples/basic.cpp?

[anupamk]

Hm, interesting :) To be sure, this is on an unmodified examples/basic.cpp?

yes it is.

[sophana]

I confirm same behavior on example minimal.cpp.
On centos7 64 bits

#0  0x00007fffe4940c84 in QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject*, QEvent*) () at /lib64/libQtCore.so.4
#1  0x00007fffe2b52b2c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () at /lib64/libQtGui.so.4
#2  0x00007fffe2b594d5 in QApplication::notify(QObject*, QEvent*) () at /lib64/libQtGui.so.4
#3  0x00007fffe3bcf806 in sipQApplication::notify(QObject*, QEvent*) () at /usr/lib64/python2.7/site-packages/PyQt4/QtGui.so
#4  0x00007fffe4940b2d in QCoreApplication::notifyInternal(QObject*, QEvent*) () at /lib64/libQtCore.so.4
#5  0x00007fffe2b99994 in QWidgetPrivate::setWinId(unsigned long) () at /lib64/libQtGui.so.4
#6  0x00007fffe2be732e in QWidget::destroy(bool, bool) () at /lib64/libQtGui.so.4
#7  0x00007fffe2ba1cd0 in QWidget::~QWidget() () at /lib64/libQtGui.so.4
#8  0x00007fffe3a1aeb9 in sipQMainWindow::~sipQMainWindow() () at /usr/lib64/python2.7/site-packages/PyQt4/QtGui.so
#9  0x00007fffe3a1af2e in release_QMainWindow () at /usr/lib64/python2.7/site-packages/PyQt4/QtGui.so
#10 0x00007fffe513ff46 in forgetObject () at /usr/lib64/python2.7/site-packages/sip.so
#11 0x00007fffe5140f59 in sipWrapper_dealloc () at /usr/lib64/python2.7/site-packages/sip.so
#12 0x00007ffff7ab1173 in subtype_dealloc () at /lib64/libpython2.7.so.1.0
#13 0x00007ffff7b24adb in collect () at /lib64/libpython2.7.so.1.0
#14 0x00007ffff7b250d8 in PyGC_Collect () at /lib64/libpython2.7.so.1.0
#15 0x00007ffff7b12249 in Py_Finalize () at /lib64/libpython2.7.so.1.0
#16 0x0000000000402adf in matplotlibcpp::detail::_interpreter::~_interpreter() ()
#17 0x00007ffff6e6ce69 in __run_exit_handlers () at /lib64/libc.so.6
#18 0x00007ffff6e6ceb5 in  () at /lib64/libc.so.6
#19 0x00007ffff6e55b1c in __libc_start_main () at /lib64/libc.so.6
#20 0x00000000004017d9 in _start ()

[xizou]

This is due to some unknown conflicts between Qt-based backend and matplotlib-cpp. An easy solution is to replace the backend with GTK3Agg by setting an environment variable:

export MPLBACKEND=GTK3Agg