Realtime blit bitmap in GTK/cairo - gtk

Question

In Windows, I can blit a bitmap to a DC picked up by GetDC at any time without calling InvalidateRect issuing a WM_PAINT message. How do I port this behavior to GTK/cairo?
In a background thread, I want to
Scale a given bitmap to "best-fit" inside a window (Need to know the width and height of in pixels)
Blit the scaled image to the screen
It should not be done through the expose event (the render loop is fast so the window will be drawn in time anyway). Full logic is
Create a window
Get context of the window
Start message loop
User presses a "Start" button
A new program thread is started that checks for a stop flag. If it is false, it issues commands that update the contents of the window regularly without user interaction. Meanwhile, the message loop checks for user input.
When user presses a "Stop" button the stop flag raises causing the rendering thread to exit
When rendering thread is not running, the expose event should call the same code as the render thread.
I have tried to catch the cairo_t* cairo_obj after creating a GtkDrawingArea (I get one)
the animation thread then calls image draw repeatedly issuing
cairo_set_source_rgb(cairo_obj, 1, 0, 0);
cairo_select_font_face(cairo_obj, "Sans", CAIRO_FONT_SLANT_NORMAL,
CAIRO_FONT_WEIGHT_NORMAL);
cairo_set_font_size(cairo_obj, 40.0);
cairo_move_to(cairo_obj, 10.0, 50.0);
cairo_show_text(cairo_obj, "Disziplin ist Macht.");
This works when doing event passing but not otherwise. Are there any other calls that has to be done at the end of the drawing code swapping buffers?
If this cannot be done with GTK/cairo, are there any other toolkit that lets me do this? Is it possible under X at all?