FIX: Add macos timers to the main thread

[greglucas]

PR summary

The macos timers need to be explicitly added to the main runloop so the drawing takes place there. This causes issues if updating data from other threads and wanting the plot to update.

Fixed previously in: #25553
Which then had a regression via: #26022 which apparently uses a method that puts the timer onto the currently active thread rather than the main one. So, we need to explicitly add the timer to the main runloop.

I tried adding this as an interactive test, but couldn't get it to trigger the draws properly from the subprocess (not sure if it is because we need to set something up differently when running as python -i from a subprocess?). Any thoughts folks have for how to test this so we don't regress again would be welcome.

Same example to manually test with. Save to file, and run with python -i testfile.py. I get a segfault currently trying to draw from a separate thread, and this updates as expected now.

import random
import time
import threading
import matplotlib as mpl
import matplotlib.pyplot as plt


class Plot:

    def __init__(self):
        plt.ion()
        self.start = time.time()
        self.xdata = []
        self.ydata = []
        self.running = None
        fig = plt.figure()
        mpl.rcParams["figure.raise_window"] = True
        plt.show()
        self.axis = fig.add_subplot(111)
        self.line, = self.axis.plot([])
        threading.Thread(target=self.worker).start()

    def worker(self):
        for _ in range(50):
            self.xdata.append(len(self.xdata))
            self.ydata.append(random.random())
            self.axis.set_xlim(0, len(self.xdata))
            self.axis.set_ylim(0, max(self.ydata))
            self.line.set_data(self.xdata, self.ydata)
            time.sleep(0.1)
        print(time.time() - self.start)


if __name__ == '__main__':
    Plot()

PR checklist

• "closes #0000" is in the body of the PR description to link the related issue
• [thoughts welcome] new and changed code is tested
• [n/a] Plotting related features are demonstrated in an example
• [n/a] New Features and API Changes are noted with a directive and release note
• [n/a] Documentation complies with general and docstring guidelines