Segmentation Fault and weird errors

Applications
,
1

Code that causes the problem:

    def delete_pages(self, *_) -> None:
        self.main_stk.set_visible_child_name("main_page")
        # remove all pages from stack1
        for page in self.pages:
            page_id = self.get_page_id(page)
            page_child = self.stack1.get_child_by_name(page_id)
            self.stack1.remove(page_child)

can someone suggest a better way to remove all pages from a stack

2

If self.pages is a list model of Gtk.StackPage instances in stack1 then it’s not safe to remove items while iterating over a list.

You have to collect all pages into a separate list, and then remove them:

def delete_pages(self):
    pages = [self.get_page_id(x) for x in self.pages]
    for page_id in pages:
        w = self.stack1.get_child_by_name(page_id)
        self.stack1.remove(w)
3

in the console I still get is it normal or should I ignore it

/Users/panda/sshfs/bakery-gui.py:1599: Warning: instance with invalid (NULL) class pointer
  self.stack1.remove(w)
/Users/panda/sshfs/bakery-gui.py:1599: Warning: g_signal_handlers_disconnect_matched: assertion 'G_TYPE_CHECK_INSTANCE (instance)' failed
  self.stack1.remove(w)
/Users/panda/sshfs/bakery-gui.py:1599: Warning: instance of invalid non-instantiatable type '(null)'
  self.stack1.remove(w)
4

That’s coming from GTK itself; which version of GTK are you using?

5

image

6

Could you try this example, and see if it emits the same warning:

import gi

gi.require_version("Gtk", "4.0")
from gi.repository import GLib, Gtk

stack = Gtk.Stack()
stack.add_named(Gtk.Button(label="Hello"), "foo")
stack.add_named(Gtk.Button(label="World"), "bar")
stack.add_named(Gtk.Button(label="Goodbye"), "baz")

pages = stack.get_pages()
assert len(pages) == 3

names = [x.get_name() for x in pages]
assert len(names) == len(pages)

print(names)

for name in names:
    w = stack.get_child_by_name(name)
    stack.remove(w)

assert len(pages) == 0
7

Do you use a Gtk.StackSideBar with the Stack?

If yes, then I’m pretty sure the crash is related to this issue.

8

is there any fix it still happens

9

You haven’t answered the question from me or @gwillems, so “is there any fix” isn’t really something we can answer.

10

yes I do its called stack1_sidebar in my code

11

OK, so I’m quite sure it’s the same issue I reported.

There is a fix under review, may take a little bit of time till it gets reviewed/integrated/released…

In the meantime, you could tweak your code to keep a reference to the page, to avoid the use-after-free crash.

Maybe something like this should be enough:

        for page in self.pages:
            page_id = self.get_page_id(page)
            page_child = self.stack1.get_child_by_name(page_id)
            self.stack1.remove(page_child)
            page   # does nothing, just here to keep an active reference during remove()
12

Thanks will try this when I can
Is there a issue/merge I can track

13

It still seg faults even when calling page

14

hmm, now I’m confused…

What about this?

        for page in list(self.pages):
            page_child = page.get_child()
            self.stack1.remove(page_child)
15 
Traceback (most recent call last):
  File "/home/panda/Bakery/bakery-gui.py", line 278, in delete_pages
    page_child = page.get_child()
                 ^^^^^^^^^^^^^^
AttributeError: 'str' object has no attribute 'get_child'

here’s the code if u wanna take a deeper look

16

Ah OK, thanks, I see, I thought self.pages was a list model of Gtk.StackPages…

Can you please try this?

        for page in self.pages:
            page_id = self.get_page_id(page)
            page_child = self.stack1.get_child_by_name(page_id)
            stackpage = self.stack1.get_page(page_child)
            self.stack1.remove(page_child)
            stackpage   # does nothing, just used to keep an active reference during remove()