Using `git bisect` I've discovered the commit (b713adf27a) (https://github.com/python/cpython/commit/b713adf27a) that broke the code.

I've used one script:
```test.py
import sys
sys.path.append("/Users/basnijholt/Downloads/cpython/Lib/concurrent/futures/")
from random import random
from process import ProcessPoolExecutor
import asyncio

ioloop = asyncio.get_event_loop()

async def func(ioloop, executor):
    result = await ioloop.run_in_executor(executor, random)
    executor.shutdown(wait=False)  # bug doesn't occur when `wait=True`

if __name__ == "__main__":
    executor = ProcessPoolExecutor()
    task = ioloop.run_until_complete(func(ioloop, executor))
```
and `test2.py`
```
import pexpect
import sys

child = pexpect.spawn("python /Users/basnijholt/Downloads/cpython/test.py")
try:
    child.expect(["OSError", "AssertionError"], timeout=1)
    raise Exception
except pexpect.EOF as e:
    sys.exit(0)
```

Then did
```
git checkout master
git reset --hard 9b6c60cbce  # bad commit
git bisect start
git bisect bad
git bisect good ad2c2d380e  # good commit
git bisect run python test2.py
```

I will see if I can fix it.