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

[Phil Thompson]

On 16/06/2015 3:30 pm, Vladimir Rutsky wrote:
> On Mon, Jun 15, 2015 at 6:33 PM, Vladimir Rutsky
> <rutsky.vladimir at gmail.com> wrote:
>> 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
> 
> I have updated the example: 
> https://gist.github.com/rutsky/d6332e3354972997e938
> 
> As I see, when QQuickView is being destroyed it waits until render 
> thread
> clean ups all resources, which causes custom created QSGGeometryNode
> to be destroyed,
> which asks to lock GIL, which is still locked by main thread, so it's 
> deadlock.

Both problems should be fixed in tonight's snapshot.

I'd be interested to know how you think the ownership of the QSGNode 
returned from updatePaintNode() should be handled. Where in the docs 
does it say that Qt handles the lifetime of the node?

Thanks,
Phil