QThread vs QTcpServer feat. QTcpSocket

[ilyagoo]

hi there! this is my first post let's start!

i've read almost all posts about QThread, QTcpServer & QTcpSocket, but still have some problems.
i wanna advice in the subject & all around

the main idea is to write multithreaded app using QTcpServer & QTcpSocket.

here's little bit of code:

client class

class TClient : public QTcpSocket
{
public:
    TClient()
    {
        connect( this, SIGNAL( connected() ), this, SLOT( connectedSlot() ) );
        connect( this, SIGNAL( disconnected() ), this, SLOT( disconnectedSlot() ) );
    }
 
private slots:
    void connectedSlot() { emit connected( this ); }
    void disconnectedSlot() { emit disconnected( this ); }
 
signals:
    void connected( TClient * );
    void disconnected( TClient * );
};

class TClient : public QTcpSocket
{
public:
    TClient()
    {
        connect( this, SIGNAL( connected() ), this, SLOT( connectedSlot() ) );
        connect( this, SIGNAL( disconnected() ), this, SLOT( disconnectedSlot() ) );
    }
    
private slots:
    void connectedSlot() { emit connected( this ); }
    void disconnectedSlot() { emit disconnected( this ); }

signals:
    void connected( TClient * );
    void disconnected( TClient * );
};

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thread class

class TClientThread : public QThread
{
public:
    TClientThread( TClient *client ) : m_Client( client ) {}
    ~TClientThread()
    {
        wait();
    }
 
protected:
    void run()
    {
        connect( m_Client, SIGNAL( destroyed() ), this, SLOT( quit() ) );
        exec();
    }
 
private:
    TClient *m_Client;
};

class TClientThread : public QThread
{
public:
    TClientThread( TClient *client ) : m_Client( client ) {}
    ~TClientThread()
    {
        wait();
    }
    
protected:
    void run()
    {
        connect( m_Client, SIGNAL( destroyed() ), this, SLOT( quit() ) );
        exec();
    }
    
private:
    TClient *m_Client;
};

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server class

class TServer : public QTcpServer
{
protected:
    void incomingConnection( int socketDescriptor )
    {
        TClient *client = new TClient;
        // assuming no error
        client->setSocketDescriptor( socketDescriptor );
        connect( client, SIGNAL( connected( TClient * ) ), this, SLOT( clientConnected( TClient * ) ), Qt::QueuedConnection );
        connect( client, SIGNAL( disconnected( TClient * ) ), this, SLOT( clientDisconnected( TClient * ) ), Qt::QueuedConnection );
 
        TClientThread *thread = new TClientThread( client );
        connect( thread, SIGNAL( finished() ), this, SLOT( killThread() ) );
        client->moveToThread( thread );
        thread->start();
 
        emit clientConnected( client );
    }
 
signals:
    void clientConnected( TClient * );
    void clientDisconnected( TClient * );
 
private slots:
    void killThread()
    {
       delete sender();
    }
};

class TServer : public QTcpServer
{
protected:
    void incomingConnection( int socketDescriptor )
    {
        TClient *client = new TClient;
        // assuming no error
        client->setSocketDescriptor( socketDescriptor );
        connect( client, SIGNAL( connected( TClient * ) ), this, SLOT( clientConnected( TClient * ) ), Qt::QueuedConnection );
        connect( client, SIGNAL( disconnected( TClient * ) ), this, SLOT( clientDisconnected( TClient * ) ), Qt::QueuedConnection );
        
        TClientThread *thread = new TClientThread( client );
        connect( thread, SIGNAL( finished() ), this, SLOT( killThread() ) );
        client->moveToThread( thread );
        thread->start();

        emit clientConnected( client );
    }

signals:
    void clientConnected( TClient * );
    void clientDisconnected( TClient * );

private slots:
    void killThread()
    {
       delete sender();
    }
};

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i call client->deleteLater() in the slot connected to TServer::clientDisconnected( TClient * );

1) is the 13th line in server class good idea or not?

2) may be better to move thread creation & moving client to thread from incomingConnection() to the slot connected to TServer::clientDisconnected( TClient * ) signal?

3) i need to obtain data from clientThread from other thread. data would be represented by char *[1-16 kBytes]? client receives data uninterruptedly, another thread process this data. i don't want client to be able to know anything about extern queue or mutex...
do you know some design pattern to use in this case or with threads in general?

4) i designed client anisochronous because i wanna use it either in main or spawned thread. it has relationship with 2)

thanks for your attention

[wysota]

1) is the 13th line in server class good idea or not?

Bad idea. Never explicitely delete a sender of a signal inside slots connected to that signal. Use deleteLater() instead (it's a slot, by the way).

2) may be better to move thread creation & moving client to thread from incomingConnection() to the slot connected to TServer::clientDisconnected( TClient * ) signal?

The socket has to be created within the thread's run() method.

3) i need to obtain data from clientThread from other thread. data would be represented by char *[1-16 kBytes]? client receives data uninterruptedly, another thread process this data. i don't want client to be able to know anything about extern queue or mutex...
do you know some design pattern to use in this case or with threads in general?

Emit a signal containing a byte array with the data.

[ilyagoo]

Use deleteLater() instead (it's a slot, by the way).

connect( thread, SIGNAL( finished() ), thread, SLOT( deleteLater() ) );
thanks

The socket has to be created within the thread's run() method.

but how to use its functions? using signals? smth like this?

TClientThread::run()
{
    TClient client;
    client->setSocketDescriptor( socketDescriptor );
    // use client's functions via signals
    connect( this, SIGNAL( someThreadSignals ), &client, SLOT( someThreadSlots() ) );
 
    exec();
}

TClientThread::run()
{
    TClient client;
    client->setSocketDescriptor( socketDescriptor );
    // use client's functions via signals
    connect( this, SIGNAL( someThreadSignals ), &client, SLOT( someThreadSlots() ) );

    exec();
}

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could i have any problems in thread's destructor relating to client on the stack?

Emit a signal containing a byte array with the data

to much copies of data: when i emit signal from one thread to another Qt produces QEvent with the copy of QByteArray. i receives 16kBytes about 100 times per second, its too hard to copy all of these arrays.

[wysota]

QEvent with the copy of QByteArray. i receives 16kBytes about 100 times per second, its too hard to copy all of these arrays.

Copy of a byte array is not the same as copy of the data it carries. QByteArray is an implicitly shared class thus there is only one copy of the data in question.

[ilyagoo]

i.e. using of QByteArray instead of queues of char* wouldn't decrease app's perfomance?

and would following code be correct to your mind?

void TClient::readyReadSlot()
{
    if ( !m_HeaderProcessed )
    {
        read( reinterpret_cast< char * >( &m_PackageHeader ), sizeof( m_PackageHeader ) );
        m_PackageHeaderProcessed = true;
    }
 
    int bytesToRead = bytesAvailable();
 
    if ( bytesToRead >= m_PackageHeader.MessageSize )
    {
        QByteArray message = read( m_PackageHeader.MessageSize );
        m_PackageHeaderProcessed = false;
 
        emit dataReceived( message );
    }
    else
        // read remaining data
        emit readyRead();
 
}

void TClient::readyReadSlot()
{
    if ( !m_HeaderProcessed )
    {
        read( reinterpret_cast< char * >( &m_PackageHeader ), sizeof( m_PackageHeader ) );
        m_PackageHeaderProcessed = true;
    }
    
    int bytesToRead = bytesAvailable();
    
    if ( bytesToRead >= m_PackageHeader.MessageSize )
    {
        QByteArray message = read( m_PackageHeader.MessageSize );
        m_PackageHeaderProcessed = false;
        
        emit dataReceived( message );
    }
    else
        // read remaining data
        emit readyRead();
    
}

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and returning to:

TClientThread::run()
{
    TClient client;
    // little mistake))
    client.setSocketDescriptor( socketDescriptor );
    // use client's functions via signals
    connect( this, SIGNAL( someThreadSignals ), &client, SLOT( someThreadSlots() ) );
 
    exec();
}

TClientThread::run()
{
    TClient client;
    // little mistake))
    client.setSocketDescriptor( socketDescriptor );
    // use client's functions via signals
    connect( this, SIGNAL( someThreadSignals ), &client, SLOT( someThreadSlots() ) );
 
    exec();
}

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i introduced signal TServer::clientDisconnected( TClient * ) because i need some information about disconnected client, for example, peerAddress & peerPort. this suggests me to use following code:

TClientThread::run()
{
    m_Client = new TClient;
    m_Client->setSocketDescriptor( socketDescriptor );
    // use client's functions via signals
    connect( this, SIGNAL( someThreadSignals ), m_Client, SLOT( someThreadSlots() ) );
 
    exec();
}

TClientThread::run()
{
    m_Client = new TClient;
    m_Client->setSocketDescriptor( socketDescriptor );
    // use client's functions via signals
    connect( this, SIGNAL( someThreadSignals ), m_Client, SLOT( someThreadSlots() ) );
 
    exec();
}

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but how can i finish thread correct now?

[wysota]

i.e. using of QByteArray instead of queues of char* wouldn't decrease app's perfomance?

No. At least not in any noticable way.

and would following code be correct to your mind?

The first "if" block is very C-ish. IMO you should read the header into a byte array. The rest seems fine.

but how can i finish thread correct now?

I don't see your point...

By the way, are you sure you need threads at all? So far I see no reason to use them in your situation.

[ilyagoo]

returning to my phrase:

i introduced signal TServer::clientDisconnected( TClient * ) because i need some information about disconnected client, for example, peerAddress & peerPort.

i introduced signal TServer::clientDisconnected( TClient * ) because i need some information about disconnected client, for example, peerAddress & peerPort.

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would it be correct to call client->peerPort() in the slot connected to aforesaid signal if this call and client are in different threads?