Windows: fix object destruction order when terminating helper threads

Windows implementation of QLowEnergyController is using helper threads
to perform device connection and characteristics read for services.

In both cases a new QObject-derived class instance is created and moved
to a helper QThread. A QThread::finished signal was used to destroy both
the helper thread and the object. This was creating a situation when the
order of destruction for a thread and a nested object was not specified.
In practice that could lead to hangs when reading multiple service
characteristics, which is specially seen on Windows 11.

This patch uses QThread::finished signal to destroy only the nested
object. Later on, the object's QObject::destroyed signal is used to
destroy the thread itself.

Task-number: QTBUG-97578
Change-Id: Ic973b835496b6098d47cd1e124315903c143e3e1
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>
(cherry picked from commit 981e3f10f48580641f5e2365953ec8a17b5c96a2)

2 files changed, 3 insertions, 3 deletions

diff --git a/src/bluetooth/qlowenergycontroller_winrt.cpp b/src/bluetooth/qlowenergycontroller_winrt.cpp
index 9109102e..6d8898e9 100644
--- a/src/bluetooth/qlowenergycontroller_winrt.cpp
+++ b/src/bluetooth/qlowenergycontroller_winrt.cpp
@@ -642,8 +642,8 @@ void QLowEnergyControllerPrivateWinRT::discoverServiceDetails(const QBluetoothUu
     QThread *thread = new QThread;
     worker->moveToThread(thread);
     connect(thread, &QThread::started, worker, &QWinRTLowEnergyServiceHandler::obtainCharList);
-    connect(thread, &QThread::finished, thread, &QObject::deleteLater);
     connect(thread, &QThread::finished, worker, &QObject::deleteLater);
+    connect(worker, &QObject::destroyed, thread, &QObject::deleteLater);
     connect(worker, &QWinRTLowEnergyServiceHandler::charListObtained, this,
             [this](const QBluetoothUuid &service, QHash<QLowEnergyHandle, QLowEnergyServicePrivate::CharData> charList
             , QVector<QBluetoothUuid> indicateChars
diff --git a/src/bluetooth/qlowenergycontroller_winrt_new.cpp b/src/bluetooth/qlowenergycontroller_winrt_new.cpp
index 5f8d5de5..e90073a4 100644
--- a/src/bluetooth/qlowenergycontroller_winrt_new.cpp
+++ b/src/bluetooth/qlowenergycontroller_winrt_new.cpp
@@ -711,8 +711,8 @@ void QLowEnergyControllerPrivateWinRTNew::connectToDevice()
     connect(this, &QLowEnergyControllerPrivateWinRTNew::abortConnection, worker,
             &QWinRTLowEnergyConnectionHandler::handleDeviceDisconnectRequest);
     connect(thread, &QThread::started, worker, &QWinRTLowEnergyConnectionHandler::connectToDevice);
-    connect(thread, &QThread::finished, thread, &QObject::deleteLater);
     connect(thread, &QThread::finished, worker, &QObject::deleteLater);
+    connect(worker, &QObject::destroyed, thread, &QObject::deleteLater);
     connect(worker, &QWinRTLowEnergyConnectionHandler::errorOccurred, this,
             [this](const QString &msg) { handleConnectionError(msg.toUtf8().constData()); });
     connect(worker, &QWinRTLowEnergyConnectionHandler::deviceConnected, this,
@@ -1166,8 +1166,8 @@ void QLowEnergyControllerPrivateWinRTNew::discoverServiceDetails(const QBluetoot
     QThread *thread = new QThread;
     worker->moveToThread(thread);
     connect(thread, &QThread::started, worker, &QWinRTLowEnergyServiceHandlerNew::obtainCharList);
-    connect(thread, &QThread::finished, thread, &QObject::deleteLater);
     connect(thread, &QThread::finished, worker, &QObject::deleteLater);
+    connect(worker, &QObject::destroyed, thread, &QObject::deleteLater);
     connect(worker, &QWinRTLowEnergyServiceHandlerNew::errorOccured,
             this, &QLowEnergyControllerPrivateWinRTNew::handleServiceHandlerError);
     connect(worker, &QWinRTLowEnergyServiceHandlerNew::charListObtained, this,