Details
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Bug
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Resolution: Unresolved
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P3: Somewhat important
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None
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5.14.0 RC2
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None
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Windows 10
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Windows
Description
Actual QT I have: QT 5.14.1
I have a QAxObject* instance (custom local COM server) I a try to connect:
const auto connection = connect(instance, SIGNAL(exception(int, const QString&, const QString&, const QString&)), SLOT(OnScannerException(int, const QString&, const QString& , const QString&)));
I do this in order to detect possible COM errors internally reported by QT to the client.
At the time I call that line the QAxObject instance, the underlying COM server of that is in an error state (The RPC server is unavailable) so I expect that the returned MetaObject::Connection
will return false when evaluated to bool but that does not happen (I also won't receive any exception signal from instance to know that it is not available)
If I debug QObject::connect source code I have this (see screenshot from Visual Studio, copy pasted code after all):
// code placeholder QMetaObject::Connection QObject::connect(const QObject *sender, const char *signal, const QObject *receiver, const char *method, Qt::ConnectionType type) { if (sender == nullptr || receiver == nullptr || signal == nullptr || method == nullptr) { qWarning("QObject::connect: Cannot connect %s::%s to %s::%s", sender ? sender->metaObject()->className() : "(nullptr)", (signal && *signal) ? signal+1 : "(nullptr)", receiver ? receiver->metaObject()->className() : "(nullptr)", (method && *method) ? method+1 : "(nullptr)"); return QMetaObject::Connection(0); } QByteArray tmp_signal_name; if (!check_signal_macro(sender, signal, "connect", "bind")) return QMetaObject::Connection(0); const QMetaObject *smeta = sender->metaObject();
when last line is called I see in debug view reported by QT library:
ReturnHr(5) tid(298) 800706BA The RPC server is unavailable.
This happens because in my case the COM server is disconnected/unavailable.
The problem is that this error is not handled internally by QObject::connect and/or possibly for QAxObject to emit exception to it's targets so that I know that COM is down.
Because of this (not knowing the state of COM instance) I might get into other errors later - not sure if all subsequent COM accesses are guaranteed to not result in undefined behaviour.