"QSocketNotifier: invalid socket 'Write' and type 26, disabling" What generates this?

[MattPhillips]

Hello,

EDIT: See 1st reply for likely solution.

I've seen this question get asked a lot but haven't found much of an answer beyond 'something is wrong with your sockets'. I've found this--thanks caduel--which says that 26 is likely an invalid file descriptor. How would an invalid descriptor come to be sent to a QSocketNotifier method? The socket in question is a QLocalSocket (one of two write sockets), and here is the code I use to send a message:

void MyClass::WriteToLog(const string& msg, MY_MSG_TYPE type)
{
    QByteArray qb;
    QDataStream out(&qb,QIODevice::WriteOnly);
    out << quint16(0) << quint8(type) << QString(msg.c_str());
    int num_bytes = qb.size() - sizeof(quint16); //Subtract four because in reading the
        //size information, the two bytes containing it are removed from the stream
        //   Also sizeof(MY_MSG_TYPE) == 8
    out.device()->seek(0);
    out << quint16(num_bytes);
 
    my_socket->write(qb);
    my_socket->flush();
}

void MyClass::WriteToLog(const string& msg, MY_MSG_TYPE type)
{
    QByteArray qb;
    QDataStream out(&qb,QIODevice::WriteOnly);
    out << quint16(0) << quint8(type) << QString(msg.c_str());
    int num_bytes = qb.size() - sizeof(quint16); //Subtract four because in reading the
        //size information, the two bytes containing it are removed from the stream
        //   Also sizeof(MY_MSG_TYPE) == 8
    out.device()->seek(0);
    out << quint16(num_bytes);

    my_socket->write(qb);
    my_socket->flush();
}

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This seems to happen more frequently the more data I send through this socket, but I don't really send that much, maybe several hundred bytes every vertical refresh (60Hz), or ~50KB/sec tops to get this.

I looked at the QSocketNotifier code and what I saw there confused me a little bit--

QSocketNotifier::QSocketNotifier(int socket, Type type, QObject *parent,
                                  const char *name)
    : QObject(parent)
{
    setObjectName(QString::fromAscii(name));
    if (socket < 0)
        qWarning("QSocketNotifier: Invalid socket specified");
    sockfd = socket;
    sntype = type;
    snenabled = true;
 
  ...
}

QSocketNotifier::QSocketNotifier(int socket, Type type, QObject *parent,
                                  const char *name)
    : QObject(parent)
{
    setObjectName(QString::fromAscii(name));
    if (socket < 0)
        qWarning("QSocketNotifier: Invalid socket specified");
    sockfd = socket;
    sntype = type;
    snenabled = true;

  ...
}

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It doesn't return the complete error message, and in the message I do get, the socket descriptor is always >0, e.g. 24 or 26.

Lastly, this crash is happening in a process launched from the one I launch using QtCreator, so I don't get any debugging output beyond what's in the subject line.

Can anybody help me with this? Thank you--

Best,
Matt