Question

In our project, we’re using gtkmm and we have several classes that extend Gtk::Window in order to display our graphical interface.

I now found out what call produces the behaviour (described in the previous revision. The question now slightly changed.)

We’re displaying one window, works like a charm.

Then, we have a window which displays various status messages. Let’s call it MessageWindow. It has a method setMessage(Glib::ustring msg) which simply calls a label’s set_text().

After some processing, we hide this window again and we now show a toolbar. Just yet another simple window, nothing crazy.

For all windows applies: The main thread calls show() on the window and creates a new thread which calls Gtk::Main::run() (without argument).

That’s how it should be, until now.

The problem starts here: The main thread now wants to call MessageWindow::setMessage("any string"). a) if I call this method, the message window reacts completely correctly. But afterwards, the toolbar-window is displayed empty. b) if I don’t call it, the message window doesn’t change the label (which is absolutely clear), and the toolbar window is displayed as it should.

Seems like the windows are messing up each other.

Now the question:

If my gui-thread is blocking in Gtk::Main::run(), how can I now change the text of a label?

We’re using gtkmm-2.4 (and no, we cannot upgrade)

Any help is appreciated.

Answer 1

Wow! That’s complicated…

First: you should not manipulate windows from several threads. That is you should have just one GUI thread that does all the GUI work, and let the other threads communicate with it.

It is theoretically possible to make it work (in Linux; in Windows it is impossible) but it is more trouble than it is worth.

Second: the line Gtk::Main main(argc, argv) is not a call, it is an object declaration. The object main should live for the duration of the program, so if you use it in a object constructor, as soon as you return from it, the object will be destroyed! Just put it at the top of the main function and forget about it.

UPDATE: My usual approach here is to create a pipe, a g_io_channel to read, and write bytes on the other end.

Other option, although I didn’t test it is to call get the GMainContext of the main thread and then g_idle_source_new() and attach that source to the main context with g_source_attach(). If you try this one and it works, please post your result here!