name : background_tasks.py #!/usr/bin/env python3 """Example of aiohttp.web.Application.on_startup signal handler""" import asyncio from typing import List import aioredis from aiohttp import web redis_listener = web.AppKey("redis_listener", asyncio.Task[None]) websockets = web.AppKey("websockets", List[web.WebSocketResponse]) async def websocket_handler(request): ws = web.WebSocketResponse() await ws.prepare(request) request.app[websockets].append(ws) try: async for msg in ws: print(msg) await asyncio.sleep(1) finally: request.app[websockets].remove(ws) return ws async def on_shutdown(app: web.Application) -> None: for ws in app[websockets]: await ws.close(code=999, message=b"Server shutdown") async def listen_to_redis(app): try: sub = await aioredis.Redis(host="localhost", port=6379) ch, *_ = await sub.subscribe("news") async for msg in ch.iter(encoding="utf-8"): # Forward message to all connected websockets: for ws in app[websockets]: await ws.send_str(f"{ch.name}: {msg}") print(f"message in {ch.name}: {msg}") except asyncio.CancelledError: pass finally: print("Cancel Redis listener: close connection...") await sub.unsubscribe(ch.name) await sub.quit() print("Redis connection closed.") async def start_background_tasks(app: web.Application) -> None: app[redis_listener] = asyncio.create_task(listen_to_redis(app)) async def cleanup_background_tasks(app): print("cleanup background tasks...") app[redis_listener].cancel() await app[redis_listener] def init(): app = web.Application() l: List[web.WebSocketResponse] = [] app[websockets] = l app.router.add_get("/news", websocket_handler) app.on_startup.append(start_background_tasks) app.on_cleanup.append(cleanup_background_tasks) app.on_shutdown.append(on_shutdown) return app web.run_app(init())