how to pass pointer to a Subclassed Qthread,in Multithread

Question

I create some class like this:

class TcpClient: public QObject
{
    public TcpClient(){}
    QSocket *socket;

    QMutex mutex;

    void write()
    {
        QMutexLocker locker(&mutex);
        socket->write();
    }
}

class SubQthread :public QThread
{
    public:
    SubQthread(TcpClient *tcp)
    {
        //
        m_tcp = tcp;

    }
    private:
    TcpClient *m_tcp;
    protected:
    void run()
    {
        m_tcp->write();
    }

}


class Widget:public QWidget
{
    public:
    Widget()
    {
        client =  new TcpClient(this);


    }
    private:
    TcpClient *client;


}

When I create multiple sub-QThreads, I pass the pointer TcpClient* to QThread. Is this a good idea? On the condition that i can ensure TcpClient* will be deleted after the app finished.

Having multiple threads communicating through the same socket is generally a bad idea, even with locking. What is your use-case? Why do all the threads need to use the same socket? Can't you have one socket and one connection *per thread*? — Some programmer dude, Feb 23 '16 at 15:36

frogatto · Answer 1 · 2016-02-23T16:04:07.533

There are multiple issues in your codes that should be addressed.

There is no QSocket class in Qt framework. I presume you are using QTcpSocket.
QTcpSockets cannot be used across multiple threads. Only their creating threads can call their methods.
The mutex object should be shared across all threads.

If you want to implement a communication channel between multiple threads, suggestions are:

QSharedMemory.
Signal/slot for small amount of data.
Manually implementing shared variables protected by mutexes.
Event loops.

Vladimir Bershov · Answer 2 · 2016-02-23T16:45:08.673

0

QTcpSocket object (and each other object of QObject derived class) lives in a thread where it was created. If you create QTcpSocket object in main (GUI) thread and want that it lives in another thread, you should use QObject::moveToThread method: qt thread with movetothread. But the right way is create socket just in working thread or use creating in necessary thread by using socket descriptor: QAbstractSocket::setSocketDescriptor()
You should be sure that you call your QTcpSocket object from the same thread that it lives. For this purpose you can use Signals & Slots with Qt::QueuedConnection

edited Feb 23 '16 at 16:45

answered Feb 23 '16 at 16:14

Vladimir Bershov

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thank you very much! I have understood your meaning,meanwhile,thanks for bearing my bad English – M.Joe Feb 24 '16 at 00:47
@M.Joe, See also: [what is the correct way to implement a `QThread`](https://stackoverflow.com/questions/4093159/what-is-the-correct-way-to-implement-a-qthread-example-please) and http://stackoverflow.com/a/35056527/4149835 – Vladimir Bershov Feb 24 '16 at 02:46

how to pass pointer to a Subclassed Qthread,in Multithread

2 Answers2