segfault with asyncio

On macOS 10.12.4, Cython 0.25.2, Python 3.6.1, if you await asyncio.sleep() <= Cython <= Python chain, it will segfault. It won’t die if you await Cython future right away, without first using Python.

Here is an example that reproduces this bug:

main.py:

WANT_CRASH = True

import asyncio
import cy_test

async def main():
    await cy_test.say()

loop = asyncio.get_event_loop()

if WANT_CRASH:
    loop.run_until_complete(main())
else:
    loop.run_until_complete(cy_test.say())

loop.close()

cy_test.pyx:

import asyncio
from py_test import py_async

async def cy_async():
    print("- this one is from Cython")

async def say():
    await cb()

async def cb(): # renaming this to "say" would prevent crash
    print("Async functions can be awaited without problem:")
    await cy_async()
    await py_async()
    print("And this will actually sleep for 3 seconds before crashing")
    await asyncio.sleep(3)
    print("I will be never output, because app has crashed already")

py_test.py:

async def py_async():
    print("- and this one is from Python")

Setup.py:

from distutils.core import setup
from distutils.extension import Extension
from Cython.Build import cythonize

setup(
    name='asyncio_cb',
    ext_modules=cythonize([
        Extension("cy_test", ["cy_test.pyx"]),
    ]),
)

Makefile:

all:
	python3 Setup.py build_ext --inplace

test:	all
	python3 main.py

clean:
	@echo Cleaning
	@rm -f cy_*.c *.o *.so *~ core
	@rm -rf build

[scoder]

Thanks for reporting back, and for the test case.

[toriningen]

@scoder, I’ve bisected this bug, and it seems that commit 3cd1e3da1766246b6b2fb053e651c1a2bed382b7 is fixing it, just as you’ve said 3 weeks ago. Sorry for misleading you, I don’t know exact reason why it had reproduced at my side since then, but most realistic explanation is that I’ve forgot to clean up lingering .c file, assuming it should be rebuilt each time.

Just to be sure, I’ve double-checked commit 829d7bbef with exact same test, it does not crash.

So, bug is seemingly fixed now, thankee-sai.