Dear Maintainer,

If one opens a folder with sufficiently large photos
(which take some time to render), open one of them,
then roll the mouse button and quickly press close
on gthumb window, gthumb crashes.

I guess this is because the gth_main_finalize() function
in gth-main.c is not thread-safe. The crash occurs when executing

_g_object_unref (gth_main->priv->extension_manager);

while another thread is still rendering the image
in _cairo_image_surface_create_from_jpeg().

Attached is sample gdb log.