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 * );
};


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;
};


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();
}
};


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();
}


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();

}



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();
}


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();
}


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.

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