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System / threads and windows

« on: May 30, 2012, 09:57:30 pm »

Hi,

I recently started to work with SFML.. seems to be a really nice and slim framework which fit's my needs..
I ran into problems when using one window in multiple threads. Background: I want to split my application into different threads:

- thread which render things on screen
- thread which processes user input
- and a few more...

but sadly I can't get it to work without the following exception:

Code: [Select]

[xcb] Unknown sequence number while processing queue
[xcb] Most likely this is a multi-threaded client and XInitThreads has not been called
[xcb] Aborting, sorry about that.
...: poll_for_event: Assertion `!xcb_xlib_threads_sequence_lost' failed.

I called XInitThreads just to be shure that this is not the root of my problem.

My code has the following structure (simplified)

class RenderThread {
  virtual void Run() {
        while (active) {
                window.setActive(true);
                glClear(GL_COLOR_BUFFER_BIT);
                window.Display();
        }
  }
}

int main() {
        sf::Window window(sf::VideoMode(1024, 768, 32), "...");
        window.SetActive(false);
        window.UseVerticalSync(true);
       
        RenderThread renderThread(window);
        renderThread.Launch();
       
       
        sf::Event event;
        while (active) {
                // wait a bit to limit frequecy to 100Hz       
                while (window.GetEvent(event)) {
                        if (event.Type == sf::Event::Closed) {
                                active = false;
                        }
                }
        }
       
        renderThread.Wait();
        window.close();
       
        return EXIT_SUCCESS;
}
 

If i add Mutex Locks i can prevent the crash but everything get's extremly slow.

My Questions

• Is the general concept okay?
• When to call setActive? (it's used to connect the opengl context to the active thread, right?)
• If the concept is bullshit, what's the right way to split eventhandling, inputhandling and rendering?
• Is there an example which demonstrates how to do it?

Full source (it's still very simple): http://pastebin.com/hJKp7iBa