Why do some QWidgets create own threads?

Hi,

I am working on a multi-threading program, which has the ability to create dynamically pages for the Tab-Widget.
These pages for the tab-widget are made of a self made page-template class.

In that template I have the whole widgets I need to create that page.
All of them are created on the Heap.

My theory is:
my_programs_core (5 Threads) + main_gui( 1 Thread)

But it is:
my theory(6 Threads) + QLineEdit of mainGUI(2 Threads) + QFileDialog for save and load (2 Threads)..

My question is:
Why do a QLineEdit located on my main-page (not on the pages for the Tab-Widget)
creates 2 Threads?

And in my template-class there are two QFileDialog instances for each page. (Load file / save file)
It means every time I create a new page with my template class I will get 2 Threads without a reason.

Can someone explain me that?

QFileDialog might be using a separate thread for populating QFileSystemModel. QLineEdit shouldn't be using separate threads unless you are using a completer with QFileSystemModel.

Thanks,

you are right

Code:

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QFileDialog *aaa = new QFileDialog(this);
 
somewhere in the code:
    model = new QFileSystemModel(q);

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But QLineEdit creates 2 Threads in my simple case.

Code:

---

QLineEdit *bbb = new QLineEdit(this);

---

Somewhere in the code in its init

Code:

---

q->setAcceptDrops(true);  //here it creates 2 threads

---

:confused::confused:

Am I the only one where QLineEdit creates threads?

QLineEdit is not using any threads, at least not by itself. Why did you think it was using threads?

donglebob is right. Instantiating QLineEdit creates threads of its own. On my system (Windows 7, Qt 4.6.2) it creates 4 threads! Actually, the threads are created inside QWidget::setAcceptDrops(), because QLineEdit calls this method inside the constructor. After a bit more debugging I've found out that the threads are created by a WinAPI function CoLockObjectExternal

Edit: I've found a way to prevent this behavior. One must call

Code:

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QLineEdit::setAcceptDrops(false);

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before the widget is shown.