GtkComboBoxText menu with many entries very slow to appear, but ~fast with area_apply_attribute_cb bottleneck disabled

Steps to reproduce

1. gcc -O2 comboboxdemo.c pkg-config --cflags --libs gtk+-3.0
2. ./a.out
3. On click on the menu of the 1st combobo it is very slow to appear (around 30 seconds)
4. But the menu of the 2nd combobox, hacked to avoid calling area_apply_attribute_cb), is reasonably fast (around 3 seconds) to appear.

Current behavior

• menu very slow to appear

Expected outcome

• A better way to map from the row in the model to the Menuitem ? The repeated get_tree_menu_get_path_item loop over results of gtk_container_get_children is crippling.

Version information

• gtk3-2.24.8
• Fedora 30

Additional information

• Ran into this problem looking into https://bugs.documentfoundation.org/show_bug.cgi?id=125388

comboboxdemo.c