Bug report

Bug summary

Calling plt.pause inside a callback crashes the GTK3Agg backend.

Code for reproduction

import matplotlib as mpl
mpl.use('GTK3Agg')

import matplotlib.pyplot as plt

def do_nothing(event):
    print('In callback.')
    plt.pause(1)

fig = plt.figure()
fig.canvas.mpl_connect('resize_event', do_nothing)

ax = fig.add_subplot()
ax.plot(0, 0, 'o')
plt.show()

Actual outcome

In callback.
**
Gtk:ERROR:../../../../gtk/gtkwindow.c:10698:gtk_window_present_with_time: assertion failed: (gdk_window != NULL)
Bail out! Gtk:ERROR:../../../../gtk/gtkwindow.c:10698:gtk_window_present_with_time: assertion failed: (gdk_window != NULL)
Aborted (core dumped)

Expected outcome

The graph should be plotted. No crashes should occur.

Matplotlib version

• Operating system: Linux Mint 20 (Ulyana)
• Matplotlib version: 3.3.3 (installed via pip install matplotlib)
• Matplotlib backend: GTK3Agg
• Python version: 3.8.5
• GTK version: 3.0

More Details

The problem disappears upon doing either of the following.

• Using the TkAgg backend.
• Removing the line plt.pause(1).