@anntzer @tacaswell
Hi! I have just tested the master branch on Windows and found that there is indeed a problem with the QSocketNotifier (it appeared here: #13306 (comment)). Previously, on that Windows machine, I was running my old code with QAbstractSocket which was fine, and did not test the newest version with QSocketNotifier there (my fault, sorry). I have tested on Linux, and there is no such problem there.

The code to reproduce on Windows (in Jupyter):

%matplotlib qt
from matplotlib import pyplot as plt
plt.plot([1,2])
plt.pause(.1)
plt.pause(.1)
plt.pause(.1)

The problem seems to be that if socketpair generates a socket with the same fileno value as it generated in the previous pause() call, the QSocketNotifier unexpectedly fires and hangs here:

Workaround fix:

rsock.set_blocking(False)

@sn.activated.connect
def on_signal(*args):
    try:
        signal = rsock.recv(1)  # clear the socket to re-arm the notifier
    except BlockingIOError:
        pass # false-trigger, nothing on rsock

What should we do with this? Is there a better solution?

Originally posted by @vdrhtc in #13306 (comment)