[Qt-interest] QTcpSocket.

[Predrag Manojlovic]

Bradley T. Hughes wrote:
> Shabd Swarup V wrote:
>> Hi,
>>
>> I am trying to read data off a socket on localhost and I'm using netcat
>> (nc) to simulate the server and to send messages on a particular socket.
>>
>> Following is the code snippet:
>>
>> /**
>> * Thread to detect socket data.
>>  *
>>  */
>> void Communicator::run()
>> {
> [snip]
>>
>>                 connect(socket, SIGNAL(readyRead()), this,
>> SLOT(readSocketData()));
> 
> So, you are connecting the socket's signal to the QThread subclasses
> readSocketData() slot. Be aware that your slot will be called by the
> main() thread, not your Communicator thread (because QThread has
> affinity to the thread that created the instance, not to itself).
> 
>> /**
>>  * Read data available on the socket.
>>  */
>>
>> void Communicator::readSocketData()
> [snip]
>>
>> Through this code, I am unable to capture the data from the socket, even
>> though the connection is made. Please correct me.
> 
> Several things:
> 
> 1. You don't need a thread to do asynchronous networking, Qt supports
> this out-of-the-box already without the need to complicate things with
> threads.
> 
> If you *must* use a thread, despite the above, then there are several
> things to watch out for:
> 
> 2. QThread is not affine to itself, but to the thread that created it
> (so connecting a QTcpSocket signal to a QThread subclasses slot is
> crossing thread boundaries and will cause concurrent access problems).
> 3. For QTcpSocket to be able to emit its signals, you have to run the
> eventloop in your thread. You do this by calling QThread::exec() in your
> run reimplementation. Note that QThread::run()'s default implementation
> does this starting with Qt 4.4.
> 4. I would recommend against subclassing QThread and suggest that you
> subclass QObject instead. This makes your class more general and easier
> to reuse. Like I mentioned above, you don't have to complicate things by
> subclassing QThread. If you *absolutely* must use threads, then this can
> be achieved by doing something like this:
> 
>     Communicator *c = new Communicator(...);
>     QThread *thread = new QThread(this);
>     c->moveToThread(thread);
>     connect(c, SIGNAL(finished()), thread, SLOT(quit()));
>     thread->start();
> 
Many people are talking about networking without threads. I think that
it is not possible always to avoid threads.
Do anyone have example for small TCP chat server/client without threads?
Tnx