Bug report

Bug summary

When using Qt5Agg, Matplotlib consumes a full CPU core while an interactive window is open. The cursor repeatedly shows a "spinner" when I mouse over the canvas. This didn't used to be the case.

Code for reproduction

import matplotlib.pyplot as plt
plt.plot([1, 2], [3, 4])
plt.ion()
plt.show(block=True)

Actual outcome

One of the CPU cores is pegged at 100%. Interface is very slow and barely responsive.

Expected outcome

Should not use up 100% of a CPU core when nothing is happening.

Matplotlib version

• Operating system: Linux 4.14.8
• Matplotlib version: 2.1.1+864.g92a93d698.dirty
• Matplotlib backend: Qt5Agg
• Python version: 3.6.4

This was reproduced on both XMonad and XFCE4. Affects both python-matplotlib (2.1.1) from official Arch repos and python-matplotlib-git from AUR.