Possible hang in websocket server after send large amount of data

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I'm experience a strange bug in a aiohttp websocket server <-> browser websocket application. this app works well for small payload. When I send large data (~100MB, 4MB chunk size) to browser client, the server may hang with a low probability (<5%). when the hang happens:

1. browser client can still send data to server, server can receive them correctly.
2. server can't send any data to browser client, hangs on send_bytes method.
3. If I refresh browser (reconnect websocket), everything works again until I send large data again and trigger next hang.

the server and client runs on same localhost. This problem still exists if I use blacksheep + uvicorn (they use websockets).

My server app looks like this:

async def handle_connection(ws):
    async for msg in ws:
        ... # handle msg here, include rpc
async def event_provider(ws, event_queue):
       # receive events from another service, such as grpc call
       q_task = event_queue.get()
       wait_tasks = [q_task, shutdown_task, ...]
       while True:
            (done,
             pending) = await asyncio.wait(wait_tasks,
                                           return_when=asyncio.FIRST_COMPLETED)
            if q_task in done:
                 data = q_task.result()
                 chunk_datas: List[bytes] = some_chunkize_func(data)
                 for chunk in chunk_datas:
                      await ws.send_bytes(data)
            wait_tasks = [q_task, shutdown_task, ...]
async def serve_app(app,
                    port,
                    shutdown_ev: threading.Event,
                    async_shutdown_ev: asyncio.Event,
                    is_sync: bool = False,
                    url=None,
                    ssl_context=None):
    loop = asyncio.get_running_loop()
    runner = web.AppRunner(app)
    await runner.setup()
    site = web.TCPSite(runner, host=url, port=port, ssl_context=ssl_context)
    await site.start()
    if not is_sync:
        await async_shutdown_ev.wait()
    else:
        await _await_shutdown(shutdown_ev, loop)
        async_shutdown_ev.set()
    await runner.cleanup()
async def main():
    event_task = asyncio.create_task(event_provider)
    aiohttp_serv = web.Application(client_max_size=4 * 1024 * 1024)
    ... # add services
    grpc_async_serv = ... # create grpc asyncio service
    
    return asyncio.gather(event_task, serve_app(aiohttp_serv), grpc_async_serv)

in app above, the event send task and websocket task are run simultaneously (via asyncio.gather). Only three aiohttp apis are used in websocket service: prepare, async for msg in ws and send_bytes.
any suggestion about this problem?

python: 3.8
aiohttp: 3.8.4
OS: ubuntu 20.04