Qt, thread safety regarding UDPlink

Question

If I have a Qt's UDPlink and a writeBytes function like this:

void UDPLink::writeBytes(const char* data, qint64 size)
{
    // Broadcast to all connected systems
    for (int h = 0; h < hosts.size(); h++)
    {
        QHostAddress currentHost = hosts.at(h);
        quint16 currentPort = ports.at(h);
        socket->writeDatagram(data, size, currentHost, currentPort);
    }
}

Here the socket is a UDP socket. Is this function thread safe? That is can I call the writeBytes() function from 2 different threads?

Answer 1

The only 2 parts that may be not thread safe:

one is that is that datagrams may get interleaved (which happens anyway with UDP so no worries)

The other thing is that QUdpSocket::writeDatagram is not thread safe. So you either need to synchronize access to socket with a mutex or using the signal/slots or make a socket for each thread.

making it thread safe can be easy:

//make it a slot or invokable
void UDPLink::writeBytes(const char* data, qint64 size)
{
    if(QThread::currentThread() != thread())
    {
        QByteArray buff(data, size);//makes a copy pass in a QByteArray to avoid
        QMetaObject::invokeMethod(this, "writeBytes", Q_ARG(QByteArray, buff));
        //this forward the call to the thread that this object resides in if the calling thread is different.
        return;
    }
    for (int h = 0; h < hosts.size(); h++)
    {
        QHostAddress currentHost = hosts.at(h);
        quint16 currentPort = ports.at(h);
        socket->writeDatagram(data, size, currentHost, currentPort);
    }
}

Answer 2

答案是否定的，QUDPsocket不是线程安全的，但是是可重入的，这意味着你不能使用相同的实例从2个不同的线程调用QUDPSocket-> writeDatagram / writeBytes， 但你可以从 QUDPSocket的不同实例调用QUDPSocket-> writeDatagram / writeBytes调用