[Qt-interest] Data exchange in threads

[Tony Rietwyk]

Hi Nick, 

Instead of using signals to send back to the threads, have you tried using QCoreApplication::postEvent with your own QEvent, posted to an object that is created inside the run method of each thread?  The docs are not at all clear about this - they just say that the event will be put into 'an event loop'.  I assume this will be the thread's event loop, if the receiver object has been created within the thread.  Your server would have something like: 

MyServer::receiveMessage(threadIs, message)
{
	// Process message...

	// Send result back to thread...
	MyThread *thread = threadMap.value( threadId );
	MyEvent *event = new MyEvent( result );
	qApp->postEvent( thread->objectMember, event );
}

The thread's objectMember would look for MyEvent in its event method override.  

You could even use the same method for thread to server instead of signals.  

Hope that helps, 

Tony. 

> -----Original Message-----
> Sent: Friday, 29 April 2011 08:45 AM
> 
> So, how I did this.
> 
> When server create new thread, he connect thread's signal  
> emitMessage(threadId, message) to server's slot 
> receiveMessage(threadId,  
> message) and server's signal emitMessage(threadId, message) 
> to thread's  
> slot receiveMessage(threadId, message).
> So, when thread need to send message to another thread, he 
> emit signal  
> emitMessage with sending message and receiver's id to server. 
> Server catch  
> signal and emit signal to all threads. All threads compare 
> their ids with  
> threadId from signal and if its matching do something with 
> this message.  
> It's works, but I have doubts about performance of this 
> method. I hope my  
> system will be used by millions people and maybe exists more 
> comfortable  
> and performance method?
> 
> Best regards,
> Nick.
> 
> Tue, 26 Apr 2011 16:54:49 +0300 було написано BRM 
> <bm_witness at yahoo.com>:
> 
> > There are numerous ways, which is best depends on what you 
> are doing.
> >
> > 1. Use a modified signal/slot:
> > - include a 'client ID' in the signal
> > - the network connection is wrapped such that it knows its 
> 'client ID'
> > - only forwards data to the client if the client ID matches.
> >
> > 2. Use dedicated objects with signals/slots
> > - each object interfaces for the entire session of the client,  
> > interfacing to
> > the internal parts as necessary, not necessarily with 
> signals/slots.  
> > This will
> > require locks/etc.
> > - each object has a normal signal/slot interface to the 
> client it is  
> > servicing.
> >
> > 3. QObject->sender()
> > - when you receive a call to a certain slot, get the signal 
> sender,  
> > generate the
> > result and then send it back only to the sender.
> > - this requires that the sender() be able to be 
> qobject_cast<>() to a  
> > known
> > QObject derived class with a known interface (slot) to send 
> the data  
> > back on.
> >
> > I have used #3 for certain tasks. #2 may be more to your 
> fitting, but it
> > certainly the harder method in most cases since you have to 
> figure out  
> > the
> > locks, etc and you can't take full advantage of signals/slots.
> >
> > So as I said - it's a matter of your system design and what 
> works best.  
> > For me,
> > #3 was a simple enough solution for something where I 
> wanted one client  
> > to have
> > total control of a multi-message process but it's not necessarily  
> > correct for
> > you - and it certainly breaks signal-slot OO practices 
> (since you're not  
> > really
> > suppose to care who calls a slot).
> >
> > $0.02
> >
> > Ben
> >
> >
> >
> > ----- Original Message ----
> >> From: Николай Шатохин <n.shatokhin at gmail.com>
> >> To: "qt-interest at qt.nokia.com" <Qt-interest at qt.nokia.com>
> >> Sent: Tue, April 26, 2011 9:02:48 AM
> >> Subject: [Qt-interest] Data exchange in threads
> >>
> >> Hello.
> >>
> >> I have one server on qt4, one client on qt4 and entry 
> point on  php.
> >>
> >> Client can send data to php by json and send data to server  (this
> >> action dynamically create new thread on server). Php can 
> send data  on
> >> server too (it's no difference for server who send data). 
> So we  have
> >> two thread created dynamically - one for client, one for 
> entry  (this
> >> threads on server can be thousands or millions). So, how 
> can  entry's
> >> thread send data only for this client's thread? If I'll  you
> >> signals/slot, all threads send data to all threads and all  threads
> >> must do checking (it's signal for me or not?). It's very 
> slow. So,  can
> >> I use some quick  method?