Boost Thread Qt Application

QTTman

HI,all

I'm try to make as described in this link(with code):
http://wiki.qt.io/Boost_Thread_Qt_Application

"So, let's call "Thread A" the thread that executes the public method of my library, that performs the three lines above. A new thread is created (the "boost" one), called "Thread B", that creates an instance of QApplication, my DialogProvider, and executes event loop of QApplication, everything in the same context. "Thread A" is blocked until I'm sure that my application is started, then returns.
Some time later, a new thread, called "Thread C", wants to call a different public method that shows my widget. I just need to call
app->showMyWidget(5,3.0);
Of course, the two parameters are specified as example. "Thread C" posts a custom event (that carries on all information I need to create my widget) to QApplication event loop, that forwards it to my DialogProvider customEvent method. In that method (I'm in QApplication context, i.e. "Thread B"), I can create my widget and show it in the end, I just signal (using a QWaitCondition) that my widget is shown, so "Thread C" can return."

How can I make communication in this example with "Thread A" and "myWidget" in both direction?

SGaist

Hi and welcome to devnet,

What kind of communication do you have in mind ? What will you pass between the two threads ?

QTTman

@SGaist
Communication : I need pass QStrings. between main thread and second thread with QApp and widgets.

SGaist

How many times do you need to do that ?

QTTman

@SGaist Many times, depends on user action.
the GUI thread sends data string to the main thread -> after doing the job, main thread sends back to GUI a result string.

SGaist

What is the main thread exactly ?

QTTman

@SGaist
Programm "X" run my DLL . This is "main thread"
In DLL I try to launch Qt GUI in different thread.

JKSH

@QTTman Does your main thread contain any QObjects? If so, you can use signals and slots to pass QStrings between the 2 threads.

Otherwise, your main thread can use QMetaObject::invokeMethod() with Qt::BlockingQueuedConnection to make a function run in your Qt thread and wait for a return value: http://doc.qt.io/qt-5/qmetaobject.html#invokeMethod

QTTman

@JKSH
If I'm right, I can't use any QObject in "main thread" before than QApp is initialized in the different thread.

JKSH

@QTTman said in Boost Thread Qt Application:

If I'm right, I can't use any QObject in "main thread" before than QApp is initialized in the different thread.

Yes, you are right.

So, you can use QMetaObject::invokeMethod()