Bug summary

There are no leaks when we plt.show() figures and fire up the GUI mainloop. However, when we are calling savefig() without ever showing we are now creating singleshot Timers in the app, but the callback never gets triggered due to the event loop not being active/listening for these timers. This is then keeping a reference from the Timer to the Figure on every close, causing a leak when calling a bunch of savefig's.

xref: #19769
But, more specifically related to Timer's generically not firing.
identified debugging: #23059

Code for reproduction

import sys
import matplotlib.pyplot as plt
import numpy as np

import matplotlib
#matplotlib.use('agg')

data = np.random.rand(60, 60)

def plot_expr(plot_name):

    plt.figure(figsize=(9, 8))

    for i in range(60):
        plt.plot(data[i, :])

    plt.savefig(plot_name)

    plt.close('all')


if __name__ == "__main__":

    print(f'python: {sys.version}')
    print(f'matplotlib: {matplotlib.__version__}')
    print(f'backend: {matplotlib.get_backend()}')

    for i in range(50):
        print(f'{i}...')
        plot_expr(f'leak_{i}')

Actual outcome

Timer's don't fire. You can put a log inside the callback to verify NSLog(@"Inside callback") that the Timer gets created but doesn't trigger.

Expected outcome

Timer's should fire even if we aren't interactive.

Additional information

No response

Operating system

MacOS

Matplotlib Version

main

Matplotlib Backend

macosx

Python version

No response

Jupyter version

No response

Installation

No response