[Qt-interest] signals, sender(), and threads...

[Gordon Schumacher]

BRM wrote:
> I have a network server program that I am porting from C/C++ to Qt to take advantage of Qt's threading, networking, and signal/slot functionality.
> In the original program, each client was assigned its own handling thread.
> The Qt version is using signals and slots and threads to handle the client communications, but some of the functionality is getting brought back to slots
> in the main program (also okay, and actually resolves some other issues related to global information).
>
> Each client connection has a QTcpSocket handled in a thread. The thread is has an instance object, which is run using a QThread derived class.
> The thread uses signals/slots to communicate between things; and the instance object adds some extra functionality.
>   

In the documentation (at least for v4.5.2) they detail when sender() is
not valid.  It sounds to me like what you really want is a synchronous
notify/response between the two classes, yes?  In that case I'd suggest
connecting the "notify" signal with Qt::BlockingQueuedConnection; that
way you should not ever run into the conditions they detail above.  (You
shouldn't be using DirectConnection between threads anyway!)

An additional thought on the "response" portion... take a look at
QMetaObject::invokeMethod() - it seems like a reasonable way to allow
you to send "response" events either directly or via connect()'ed signals.