src/unix/core.c:896: uv__io_stop: Assertion `loop->watchers[w->fd] == w' failed. when opening a datagram endpoint

[matthiasblondeel]

• uvloop version: 0.9
• Python version: 3.6.1
• Platform: Linux
• Can you reproduce the bug with PYTHONASYNCIODEBUG in env?: YES

In uvloop 0.9 it looks like an issue was introduced when creating new udp endpoints.
The below code works fine with uvloop 0.8, but fails and crashes the process in uvloop 0.9

import asyncio
import uvloop
asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())

receive_addr = ('127.0.0.1', 1234)

async def crash_python():
    counter = 0
    while True:
        transport, _ = await asyncio.get_event_loop().create_datagram_endpoint(
             asyncio.Protocol, reuse_port=True, local_addr=receive_addr)
        print('started', counter)
        counter+=1
        await asyncio.sleep(0.1)
    
asyncio.get_event_loop().run_until_complete(crash_python())

On my system it takes somewhere between 10 and 90 iterations of the counter before a crash occurs.
I get the following assertion:

python: src/unix/core.c:896: uv__io_stop: Assertion `loop->watchers[w->fd] == w' failed.

[1st1]

An obvious fix is to manually call transport.close() instead of relying on GC. But uvloop shouldn't crash regardless. Looking into this.

[1st1]

Looks like the new UDP implementation is a bit racy w.r.t. GC. Ideally we should just revert to use uv_udp_t implementation, but that's blocked on #120 and libuv/leps#10.

[aptonline]

Any chance the above reference (#20829) can be investigated? After removing uvloop 0.12.0 from Home Assistant my docker container has not crashed once.