> This change introduced a leak in test_asyncio: bpo-40115.

Thanks for bringing attention to it Victor. It seems like a rather odd side effect, considering that PR-19149 had no C code and was internal to concurrent.futures and threading. I did not expect asyncio to be dependent on the executors using atexit and daemon threads.

I'll see if I can figure it out, but this one might be a bit tricky to troubleshoot.