[PyQt] [BUG] Return value of overriden QSGMaterial::createShader() impropely destroyed before use

[Vladimir Rutsky]

Hello, Phil,

I made an example that reproduces this bug:
https://gist.github.com/rutsky/d6332e3354972997e938

Plus it shows another bug: application hangs on exit on GNU/Linux.

If I attach to it with GDB I can see, that application is waiting for
some condition variable in QSGRenderLoop::cleanup().

    0  pthread_cond_wait@@GLIBC_2.3.2 () at
../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
    1  0x00007f719d0f9cc3 in QWaitCondition::wait(QMutex*, unsigned
long) () from /home/bob/Qt/5.4/gcc_64/lib/libQt5Core.so.5
    2  0x00007f719e6f0acb in ?? () from
/home/bob/Qt/5.4/gcc_64/lib/libQt5Quick.so.5
    3  0x00007f719e6f12a0 in ?? () from
/home/bob/Qt/5.4/gcc_64/lib/libQt5Quick.so.5
    4  0x00007f719e6e7268 in QSGRenderLoop::cleanup() () from
/home/bob/Qt/5.4/gcc_64/lib/libQt5Quick.so.5
    5  0x00007f719d32e049 in qt_call_post_routines() () from
/home/bob/Qt/5.4/gcc_64/lib/libQt5Core.so.5
    6  0x00007f7197dc6a66 in QApplication::~QApplication() () from
/home/bob/Qt/5.4/gcc_64/lib/libQt5Widgets.so.5
    7  0x00007f7198892768 in sipQApplication::~sipQApplication
(this=0x259ba90, __in_chrg=<optimized out>) at
sipQtWidgetspart0.cpp:301912
    8  0x00007f7198892798 in sipQApplication::~sipQApplication
(this=0x259ba90, __in_chrg=<optimized out>) at
sipQtWidgetspart0.cpp:301915
    9  0x00007f7198895f31 in release_QApplication (sipCppV=0x259ba90)
at sipQtWidgetspart0.cpp:303524
    10 0x00007f7198895fca in dealloc_QApplication
(sipSelf=0x7f7197809168) at sipQtWidgetspart0.cpp:303538
    11 0x00007f7199d5b346 in ?? () from
/home/bob/work/proplan/env/lib/python3.4/site-packages/sip.so
    12 0x00007f7199d5c5e9 in ?? () from
/home/bob/work/proplan/env/lib/python3.4/site-packages/sip.so
    13 0x0000000000515c82 in ?? ()
    14 0x00000000004fb938 in ?? ()
    15 0x0000000000511820 in ?? ()
    16 0x00000000005117fe in ?? ()
    17 0x00000000005ae979 in ?? ()
    18 0x00000000005972bd in PyErr_PrintEx ()
    19 0x0000000000596331 in PyRun_SimpleFileExFlags ()
    20 0x00000000004cb93a in Py_Main ()
    21 0x00000000004cad1f in main ()

(This issue is not reproduces in Windows, since Qt 5.4 still uses single
threaded rendering there.)


Regards,

Vladimir Rutsky