Do civilians with guns ever stop mass shootings?

Backers of laws that let pretty much all law-abiding people carry concealed guns in public places often argue that these laws will sometimes enable people to stop mass shootings. Opponents occasionally ask: If that’s so, what examples can one give of civilians armed with guns stopping such shootings? Sometimes, I hear people asking if even one such example can be found, or saying that they haven’t heard of even one such example.

A while back I posted about a few examples, but since then there have been some more, so I thought I’d note them.