The destructor of RedisQtAdapter will be called AFTER the context has been freed.
At that point, m_ctx is a dangling pointer and should not be dereferenced.
See the valgrind output of the example-qt.cpp:
==31513== 1 errors in context 1 of 1:
==31513== Invalid write of size 8
==31513== at 0x10B885: RedisQtAdapter::~RedisQtAdapter() (qt.h:77)
==31513== by 0x10B966: ExampleQt::~ExampleQt() (example-qt-fix.h:21)
==31513== by 0x10BC70: main (example-qt-fix.cpp:47)
==31513== Address 0x7a7b120 is 304 bytes inside a block of size 464 free'd
==31513== at 0x484B27F: free (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==31513== by 0x486260B: hi_free (in /home/david/hiredis_async/install/lib/libhiredis.so.1.2.1-dev)
==31513== by 0x486442F: redisFree (in /home/david/hiredis_async/install/lib/libhiredis.so.1.2.1-dev)
==31513== by 0x4860ABD: __redisAsyncFree (in /home/david/hiredis_async/install/lib/libhiredis.so.1.2.1-dev)
==31513== by 0x4860B29: redisAsyncFree (in /home/david/hiredis_async/install/lib/libhiredis.so.1.2.1-dev)
==31513== by 0x10B956: ExampleQt::~ExampleQt() (example-qt-fix.h:19)
==31513== by 0x10BC70: main (example-qt-fix.cpp:47)
==31513== Block was alloc'd at
==31513== at 0x484DCD3: realloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==31513== by 0x485EDDD: hi_realloc (in /home/david/hiredis_async/install/lib/libhiredis.so.1.2.1-dev)
==31513== by 0x485FDB7: redisAsyncInitialize (in /home/david/hiredis_async/install/lib/libhiredis.so.1.2.1-dev)
==31513== by 0x486005E: redisAsyncConnectWithOptions (in /home/david/hiredis_async/install/lib/libhiredis.so.1.2.1-dev)
==31513== by 0x486014C: redisAsyncConnect (in /home/david/hiredis_async/install/lib/libhiredis.so.1.2.1-dev)
==31513== by 0x10BA67: ExampleQt::run() (example-qt-fix.cpp:22)
==31513== by 0x10B4FC: ExampleQt::qt_static_metacall(QObject*, QMetaObject::Call, int, void**) (moc_example-qt-fix.cpp:79)
==31513== by 0x4CA3D40: QObject::event(QEvent*) (in /opt/Qt5.12.12/5.12.12/gcc_64/lib/libQt5Core.so.5.12.12)
==31513== by 0x4C77312: QCoreApplication::notifyInternal2(QObject*, QEvent*) (in /opt/Qt5.12.12/5.12.12/gcc_64/lib/libQt5Core.so.5.12.12)
==31513== by 0x4C79DC6: QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) (in /opt/Qt5.12.12/5.12.12/gcc_64/lib/libQt5Core.so.5.12.12)
==31513== by 0x4CCF012: postEventSourceDispatch(_GSource*, int (*)(void*), void*) (in /opt/Qt5.12.12/5.12.12/gcc_64/lib/libQt5Core.so.5.12.12)
==31513== by 0x5AEED3A: g_main_context_dispatch (in /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0.7200.4)
==31513==
==31513== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
Nulling redisAsyncContext.ev.data at that point makes no sense anyway, since the context has been freed already.
So the proposed fix is to remove the offending code
The destructor of RedisQtAdapter will be called AFTER the context has been freed. At that point, m_ctx is a dangling pointer and should not be dereferenced.
See the valgrind output of the example-qt.cpp:
Nulling redisAsyncContext.ev.data at that point makes no sense anyway, since the context has been freed already. So the proposed fix is to remove the offending code