await websocket.recv() block the coroutine loop.

[liyi-lee]

This problem is not consistently reproducible.

I have a client program that, when started, receives information from the server, processes it, and then sends the result back to the server. However, I have encountered an issue: after the client processes a batch of data, it enters a frozen state where all coroutines stop running. It remains in this state until I press Ctrl+C to exit. By this time, the server has already disconnected due to not receiving a 'pong' in time. The client then restarts the connection and the cycle repeats.

Here is my sample code.

class WebSocketClient:
    def __init__(self, uri):
        self.uri = uri
        self.websocket = None
        self.lock = asyncio.Lock()

    async def connect(self):
        while True:
            try:
                self.websocket = await websockets.connect(self.uri)
                break
            except OSError as e:
                logging.error()

    async def send_message(self, message):
        if message:
            async with self.lock:
                await self.websocket.send(message)

    async def listen(self):
        try:
            while True:
                message = await self.websocket.recv()
                logging.info(f"Message from {self.uri}: {message}")
                # await anthor coroutine
                # send message
                await send_message("xxx")
        except Exception as e:
            logging.error(f"listen error :{e} , stopping listen task.")
            raise


    async def run(self, interval):
        while True:
            listen_task = None
            try:
                await self.connect()
                listen_task = asyncio.create_task(self.listen())
                await listen_task
            finally:
                if self.websocket and not self.websocket.closed:
                    await self.websocket.close()


async def main():
    client = WebSocketClient(server_str, plugin)
    await client.run()

if __name__ == "__main__":
    asyncio.run(main(), debug=True)

The log is probably something like this.

2024-05-20 21:11:00 | websockets.client | DEBUG | < PING '' [0 bytes]
2024-05-20 21:11:00 | websockets.client | DEBUG | > PONG '' [0 bytes]
2024-05-20 21:11:30 | websockets.client | DEBUG | < PING '' [0 bytes]
2024-05-20 21:11:30 | websockets.client | DEBUG | > PONG '' [0 bytes]
2024-05-20 21:12:00 | websockets.client | DEBUG | < PING '' [0 bytes]

At this point, it entered a frozen state. When I press Ctrl+C, the following log is output.

2024-05-20 21:15:00 | websockets.client | DEBUG | > PONG '' [0 bytes]
2024-05-20 21:15:00 | websockets.client | DEBUG | < PING '' [0 bytes]
2024-05-20 21:15:00 | websockets.client | DEBUG | > PONG '' [0 bytes]
2024-05-20 21:15:00 | websockets.client | DEBUG | < PING '' [0 bytes]
2024-05-20 21:15:00 | websockets.client | DEBUG | > PONG '' [0 bytes]

It seems that when the log mentioned above is being output, only the coroutine for await websocket.recv() is running. It appears that this is causing a blockage in the entire coroutine loop. Even when I replaced it with await asyncio.wait_for(websocket.recv(), 60), it still causes a blockage.

Please help me solve this problem. Thanks

[Aymeric Augustin]

This doesn't look like a bug in websockets. With the info you provided, I have no hypothesis of what may cause the issue you're seeing.

There's at least two clear problems in the code but I don't have enough information to tell if and how they could lead to blocking:

• every time you create a new connection, you run a new coroutine runningself.listen and it isn't guaranteed that self.listen terminates when that connection closes (because the definition of self.websocket can change while self.listen is running)

• the lock is completely unnecessary