Do QTcpSocket or QSslSocket automatically create thread for reading/writing?

Despite not using `std::thread` or `QThread` anywhere, still getting following problems:
1. Always a runtime debug error log from Qt:

Quote:

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QObject::connect: Cannot queue arguments of type 'QAbstractSocket::SocketError'
(Make sure 'QAbstractSocket::SocketError' is registered using qRegisterMetaType().)

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2. Intermittent crash on `TcpSocket::flush()` method; I use this method to make sure that the TCP is written immediately; Now sometimes the app crashes exactly at this method with `SIGPIPE`

Upon searching internet, found that people suggest that to fix 1st problem (i.e. the meta error), I need to register using qRegisterMetaType(), when we have multiple threads.
Same multithreading is referred as a cause for the 2nd problem as well; see this and this.

But I don't have more than 1 thread!
My socket code looks like below:

Code:

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struct Socket : public QSslSocket
{
  Q_OBJECT public:
 
  void ConnectSlots ()
  {
    const auto connectionType = Qt::QueuedConnection;
    connect(this, SIGNAL(readyRead()), this, SLOT(ReceiveData()), connectionType);
    connect(this, SIGNAL(disconnected()), this, SLOT(Disconnected()), connectionType);
    connect(this, SIGNAL(error(QAbstractSocket::SocketError)),
                 this, SLOT(Error(QAbstractSocket::SocketError)), connectionType);
    //                           ^^^^^^^ error comes whether I comment this or not
  }
 
  public slots:
  void ReceiveData () { ... }
  void Disconnected () { ... }
  void Error () { ... }
}

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Question: Is Qt creating any internal thread by itself for read/write purpose? (I hope not). How to fix above 2 issues?

Registering the enums is a must if you want them to be used with signal/slots.
It has nothing to do with threads.

Quote:

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Is Qt creating any internal thread by itself for read/write purpose? (I hope not)

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No, they don't.