socket.send() raised exception

[pohmelie]

Sometimes, when trying to write to closed socket there is no ConnectionResetError exception, but some message to console "socket.send() raised exception" and program continue to execute as nothing happens. I don't understand the nature of this issue, but I saw same problem in stackoverflow questions. Here is code to reproduce, and this work on 3.4.2, 3.4.3 and 3.5.0 on my ubuntu 14.04:

import asyncio
import time


host, port = "127.0.0.1", 8888
data_size = 8192


@asyncio.coroutine
def write_worker():

    reader, writer = yield from asyncio.open_connection(host, port)
    while True:

        writer.write(b"-" * data_size)
        yield from writer.drain()


def read_worker(reader, writer):

    start = time.perf_counter()
    while time.perf_counter() - start < 0.5:

        data = yield from reader.read(data_size)

    writer.close()


if __name__ == "__main__":

    try:

        loop = asyncio.get_event_loop()
        coro = asyncio.start_server(read_worker, host, port)
        server = loop.run_until_complete(coro)
        loop.run_until_complete(write_worker())

    except KeyboardInterrupt:

        server.close()

    print("done")

If we put yield between writer.write(b"-" * data_size) and yield from writer.drain() then problem go away, but we can't use yield in 3.5.0 with coroutines.
What to do:

• Left as is (:-1:)
• use yield from asyncio.sleep(0)
• something else?

[rsichnyi]

The weird thing is that problem goes away also in case if you put something like print(data) after yield from reader.read(data_size) or yield from asyncio.sleep(0) before closing writer in read_worker(). Tried to run server and client in different processes (just to avoid running in same loop) - mentioned changes in server code fixes the issue as well...

[pohmelie]

What a hell?! 😃
So you think it is enough to make some «magic» on server side? Cause I think anyone (client or server) can close connection, while another side will writing to socket.

[rsichnyi]

Idk honestly, but it feels like asyncio bug, "socket.send() raised exception" is the warning which, afaik, should never be encountered under normal circumstances.

[pohmelie]

python/asyncio#248
python/asyncio#257
@rsichny, you're right. That's asyncio issue.

[rsichnyi]

python/asyncio#280

[pohmelie]

🎉