We have a GUI application that deadlocks with PyTango 10.1.5 and 10.3.1; it does not reproduce with 10.0.4. The GUI thread holds the GIL while Python decrefs an AttributeProxy. Its C++ destructor enters `DeviceProxy::~DeviceProxy()` and `unsubscribe_all_events()`, then waits for cppTango’s event-subscription lock. Meanwhile, `EventConsumerKeepAliveThread` holds that cppTango lock while delivering subscription feedback and waits to acquire the GIL for the Python event callback. - GUI thread: GIL -> cppTango event lock - Event thread: cppTango event lock -> GIL This creates a deadlock. The likely regression is the pybind11 `AttributeProxy` binding. PyTango 10.0.4 created `AttributeProxy` objects with `DeleterWithoutGIL`, so native destruction happened with the GIL released. The current [`ext/client/attribute_proxy.cpp`](https://gitlab.com/tango-controls/pytango/-/blob/4fe5e08d7f9f1fbe2e40326cfa5eb6e3dd8e1a73/ext/client/attribute_proxy.cpp) doesn't do this. `DeviceProxy` already has the corresponding protection, added in commit af0b557c. `AttributeProxy` needs the same. Suggested fix: return a `std::shared_ptr<Tango::AttributeProxy>` with `DeleterWithoutGIL` from every construction path, including the copy and unpickle paths. ```cpp return std::shared_ptr<Tango::AttributeProxy>( new Tango::AttributeProxy(name.c_str()), DeleterWithoutGIL()); ``` <details> <summary>Example stack trace</summary> Just the two threads that were deadlocked: ``` Traceback for thread 354084 (app) [Waiting for the GIL] (most recent call last): (C) File "???", line 0, in __clone (/usr/lib64/libc-2.28.so) (C) File "???", line 0, in start_thread (/usr/lib64/libpthread-2.28.so) (C) File "???", line 0, in omni_thread_wrapper (/opt/conda/envs/app/lib/libomnithread.so.4.4) (C) File "/usr/local/src/conda/cpptango-10.1.2/src/client/eventkeepalive.cpp", line 631, in Tango::EventConsumerKeepAliveThread::run_undetached(void*) (/opt/conda/envs/app/lib/libtango.so.10.1.2) (C) File "/usr/local/src/conda/cpptango-10.1.2/src/client/eventkeepalive.cpp", line 835, in Tango::EventConsumerKeepAliveThread::not_conected_event(Tango::PointerWithLock<Tango::EventConsumer>&, long, Tango::PointerWithLock<Tango::EventConsumer>&) [clone .cold] (/opt/conda/envs/app/lib/libtango.so.10.1.2) (C) File "/usr/local/src/conda/cpptango-10.1.2/src/client/eventkeepalive.cpp", line 1805, in Tango::EventConsumerKeepAliveThread::subscription_feedback(__gnu_cxx::__normal_iterator<Tango::event_not_connected*, std::vector<Tango::event_not_connected, std::allocator<Tango::event_not_connected> > > const&, std::optional<Tango::DevFailed>, Tango::EventReason, long const&) (/opt/conda/envs/app/lib/libtango.so.10.1.2) (C) File "/usr/local/src/conda/cpptango-10.1.2/src/include/tango/client/event.h", line 748, in void Tango::safe_execute_callback_or_store_data<Tango::FwdEventData>(Tango::CallBack*, Tango::FwdEventData*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Tango::EventQueue*) (inlined) (/opt/conda/envs/app/lib/libtango.so.10.1.2) (C) File "/usr/local/src/conda/cpptango-10.1.2/src/include/tango/client/event.h", line 691, in void Tango::safe_execute_callback_or_store_data<Tango::FwdEventData>(Tango::CallBack*, Tango::FwdEventData*, bool, Tango::FwdEventData*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Tango::EventQueue*) (/opt/conda/envs/app/lib/libtango.so.10.1.2) (C) File "/usr/local/src/conda/python-3.11.15/Python/ceval_gil.h", line 231, in take_gil (/opt/conda/envs/app/bin/python3.11) (C) File "/usr/local/src/conda/python-3.11.15/Python/condvar.h", line 73, in PyCOND_TIMEDWAIT (inlined) (/opt/conda/envs/app/bin/python3.11) (C) File "???", line 0, in pthread_cond_timedwait@@GLIBC_2.3.2 (/usr/lib64/libpthread-2.28.so) Traceback for thread 353997 (app) [Has the GIL] (most recent call last): (C) File "/usr/local/src/conda/python-3.11.15/Parser/pegen.c", line 422, in _start (/opt/conda/envs/app/bin/python3.11) (C) File "???", line 0, in __libc_start_main (/usr/lib64/libc-2.28.so) (C) File "/usr/local/src/conda/python-3.11.15/Modules/main.c", line 738, in Py_BytesMain (/opt/conda/envs/app/bin/python3.11) (C) File "/usr/local/src/conda/python-3.11.15/Modules/main.c", line 684, in Py_RunMain (/opt/conda/envs/app/bin/python3.11) (C) File "/usr/local/src/conda/python-3.11.15/Modules/main.c", line 605, in pymain_run_python (inlined) (/opt/conda/envs/app/bin/python3.11) (C) File "/usr/local/src/conda/python-3.11.15/Modules/main.c", line 379, in pymain_run_file (inlined) (/opt/conda/envs/app/bin/python3.11) (C) File "/usr/local/src/conda/python-3.11.15/Modules/main.c", line 360, in pymain_run_file_obj (inlined) (/opt/conda/envs/app/bin/python3.11) (C) File "/usr/local/src/conda/python-3.11.15/Python/pythonrun.c", line 1657, in pyrun_file (/opt/conda/envs/app/bin/python3.11) (C) File "/usr/local/src/conda/python-3.11.15/Python/pythonrun.c", line 1762, in run_mod (/opt/conda/envs/app/bin/python3.11) (C) File "/usr/local/src/conda/python-3.11.15/Python/pythonrun.c", line 1741, in run_eval_code_obj (/opt/conda/envs/app/bin/python3.11) (Python) File "/opt/conda/envs/app/bin/appi", line 10, in <module> sys.exit(main()) (Python) File "/opt/conda/envs/app/lib/python3.11/site-packages/app/app.py", line 1078, in main sys.exit(app.exec_()) (Python) File "/opt/conda/envs/app/lib/python3.11/site-packages/taurus/qt/qtgui/application/taurusapplication.py", line 390, in exec_ ret = Qt.QApplication.exec_(*args, **kwargs) (C) File "/usr/local/src/conda/python-3.11.15/Objects/methodobject.c", line 553, in cfunction_call (/opt/conda/envs/app/bin/python3.11) (C) File "???", line 0, in meth_QApplication_exec_ (/opt/conda/envs/app/lib/python3.11/site-packages/PyQt5/QtWidgets.abi3.so) (C) File "???", line 0, in QCoreApplication::exec() (/opt/conda/envs/app/lib/libQt5Core.so.5.15.15) (C) File "???", line 0, in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) (/opt/conda/envs/app/lib/libQt5Core.so.5.15.15) (C) File "???", line 0, in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (/opt/conda/envs/app/lib/libQt5Core.so.5.15.15) (C) File "???", line 0, in g_main_context_iteration (/opt/conda/envs/app/lib/libglib-2.0.so.0.8800.3) (C) File "???", line 0, in g_main_context_iterate_unlocked.isra.0 (/opt/conda/envs/app/lib/libglib-2.0.so.0.8800.3) (C) File "???", line 0, in g_main_dispatch (/opt/conda/envs/app/lib/libglib-2.0.so.0.8800.3) (C) File "???", line 0, in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) (/opt/conda/envs/app/lib/libQt5Core.so.5.15.15) (C) File "???", line 0, in QCoreApplication::notifyInternal2(QObject*, QEvent*) (/opt/conda/envs/app/lib/libQt5Core.so.5.15.15) (C) File "???", line 0, in sipQApplication::notify(QObject*, QEvent*) (/opt/conda/envs/app/lib/python3.11/site-packages/PyQt5/QtWidgets.abi3.so) (C) File "???", line 0, in QApplicationPrivate::notify_helper(QObject*, QEvent*) (/opt/conda/envs/app/lib/libQt5Widgets.so.5.15.15) (C) File "???", line 0, in QObject::event(QEvent*) (/opt/conda/envs/app/lib/libQt5Core.so.5.15.15) (C) File "???", line 0, in PyQtSlotProxy::qt_metacall(QMetaObject::Call, int, void**) (/opt/conda/envs/app/lib/python3.11/site-packages/PyQt5/QtCore.abi3.so) (C) File "???", line 0, in PyQtSlotProxy::unislot(void**) (/opt/conda/envs/app/lib/python3.11/site-packages/PyQt5/QtCore.abi3.so) (C) File "???", line 0, in PyQtSlot::invoke(void**, _object*, void*, bool) const (/opt/conda/envs/app/lib/python3.11/site-packages/PyQt5/QtCore.abi3.so) (C) File "???", line 0, in PyQtSlot::call(_object*, _object*) const (/opt/conda/envs/app/lib/python3.11/site-packages/PyQt5/QtCore.abi3.so) (Python) File "/opt/conda/envs/app/lib/python3.11/site-packages/taurus/qt/qtcore/taurusqlistener.py", line 134, in filterEvent self.handleEvent(*r) (Python) File "/opt/conda/envs/app/lib/python3.11/site-packages/app/taurusextra/customtaurusplots.py", line 355, in handleEvent self.newSpectrumObtained.emit(evt_value) (C) File "???", line 0, in pyqtBoundSignal_emit (/opt/conda/envs/app/lib/python3.11/site-packages/PyQt5/QtCore.abi3.so) (C) File "???", line 0, in PyQtSlotProxy::qt_metacall(QMetaObject::Call, int, void**) (/opt/conda/envs/app/lib/python3.11/site-packages/PyQt5/QtCore.abi3.so) (C) File "???", line 0, in PyQtSlotProxy::unislot(void**) (/opt/conda/envs/app/lib/python3.11/site-packages/PyQt5/QtCore.abi3.so) (C) File "???", line 0, in PyQtSlot::invoke(void**, _object*, void*, bool) const (/opt/conda/envs/app/lib/python3.11/site-packages/PyQt5/QtCore.abi3.so) (C) File "???", line 0, in PyQtSlot::call(_object*, _object*) const (/opt/conda/envs/app/lib/python3.11/site-packages/PyQt5/QtCore.abi3.so) (C) File "/usr/local/src/conda/python-3.11.15/Include/object.h", line 602, in Py_XDECREF (inlined) (/opt/conda/envs/app/bin/python3.11) (C) File "/usr/local/src/conda/python-3.11.15/Include/object.h", line 538, in Py_DECREF (inlined) (/opt/conda/envs/app/bin/python3.11) (C) File "/usr/local/src/conda/python-3.11.15/Objects/typeobject.c", line 1433, in subtype_dealloc (/opt/conda/envs/app/bin/python3.11) (C) File "/usr/local/src/conda/python-3.11.15/Include/object.h", line 602, in Py_XDECREF (inlined) (/opt/conda/envs/app/bin/python3.11) (C) File "/usr/local/src/conda/python-3.11.15/Include/object.h", line 538, in Py_DECREF (inlined) (/opt/conda/envs/app/bin/python3.11) (C) File "/usr/local/src/conda/cpptango-10.1.2/src/client/attr_proxy.cpp", line 783, in Tango::AttributeProxy::~AttributeProxy() (/opt/conda/envs/app/lib/libtango.so.10.1.2) (C) File "/usr/local/src/conda/cpptango-10.1.2/src/client/attr_proxy.cpp", line 782, in Tango::AttributeProxy::~AttributeProxy() (/opt/conda/envs/app/lib/libtango.so.10.1.2) (C) File "/usr/local/src/conda/cpptango-10.1.2/src/client/devapi_base.cpp", line 3200, in Tango::DeviceProxy::~DeviceProxy() (/opt/conda/envs/app/lib/libtango.so.10.1.2) (C) File "/usr/local/src/conda/cpptango-10.1.2/src/client/devapi_base.cpp", line 3177, in Tango::DeviceProxy::~DeviceProxy() (/opt/conda/envs/app/lib/libtango.so.10.1.2) (C) File "/usr/local/src/conda/cpptango-10.1.2/src/client/devapi_base.cpp", line 3210, in Tango::DeviceProxy::unsubscribe_all_events() (/opt/conda/envs/app/lib/libtango.so.10.1.2) (C) File "/usr/local/src/conda/cpptango-10.1.2/src/client/zmqeventconsumer.cpp", line 3499, in Tango::ZmqEventConsumer::get_subscribed_event_ids(Tango::DeviceProxy*, std::vector<int, std::allocator<int> >&) (/opt/conda/envs/app/lib/libtango.so.10.1.2) (C) File "/usr/local/src/conda/cpptango-10.1.2/src/include/tango/server/readers_writers_lock.h", line 191, in ReaderLock::ReaderLock(ReadersWritersLock&) (inlined) (/opt/conda/envs/app/lib/libtango.so.10.1.2) (C) File "/usr/local/src/conda/cpptango-10.1.2/src/include/tango/server/readers_writers_lock.h", line 70, in ReadersWritersLock::readerIn() (inlined) (/opt/conda/envs/app/lib/libtango.so.10.1.2) (C) File "???", line 0, in omni_condition::wait() (/opt/conda/envs/app/lib/libomnithread.so.4.4) (C) File "???", line 0, in pthread_cond_wait@@GLIBC_2.3.2 (/usr/lib64/libpthread-2.28.so) ``` </details>