[Interest] Calling QT Class method from pthread thread

[Thiago Macieira]

On Wednesday, 4 October 2017 08:41:32 PDT Gonzalo Aguilar Delgado wrote:
> Hello Thiago,
> 
> Hope you can see something...

Thanks.

Did you also run this under valgrind? Maybe using a prelinker? Some pointers 
are funny.

> #0  0x00007ffff61d7cec in QMetaObject::activate(QObject*, QMetaObject
> const*, int, void**) (sender=0x7fffd15dddf0, m=<optimized out>,
> local_signal_index=<optimized out>, argv=<optimized out>) at
> kernel/qobject.cpp:3513

The "this" pointer passes the smell detection: it's an address on a thread's 
stack (unlikely to be the main thread) or a thread's memory pool and is 
aligned to 16.

> #1  0x000055555555ea29 in MQMessageManager::cardValidationSuccess()
> (this=0x7fffd15dddf0) at moc_mqmessagemanager.cpp:134
> #2  0x000055555555d785 in MQMessageManager::processMessage(_SG64ZeroMQ*,
> _ThriftStruct*, _GError**) (this=0x7fffd15dddf0, mq=0x555555a59d40,
> message=0x7fffd400f380, error=0x555555a59d40) at ../mqmessagemanager.cpp:114

Those pointers starting with lots of 5 are the funny ones I mentioned.

> array = {static shared_null = {ref = {_q_value = 299}, alloc = 0, size = 0,
> data = 0x7ffff65297b8 <QByteArray::shared_null+24> "", array = ""}, static
> shared_empty = {ref = {_q_value = 3}, alloc = 0, size = 0, data =
> 0x7ffff6529798 <QByteArray::shared_empty+24> "", array = ""}, d =
> 0x7fffc00049c0}

This variable is wrong. The shared_null in Qt 5 has a counter always equal to 
0. It should never grow from it, so 299 and 3 are definitely wrong. The 
debugging information is coming from Qt 4 because of the presence of "array" 
member.

You're either using Qt 4 or you're mixing Qt 4 and Qt 5 in the same 
aplication. I'm going to stop here until you confirm you're only using Qt 5 
(minimum 5.6). I'm not going to support a Qt 4 application.

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center