This is a copy of @vercel/[email protected] except with 2 things changed in vc_init.py:

1. Uses a shared event loop.

Vercel does asyncio.new_event_loop() every new request, which leads to RuntimeError being raised if 2 requests use/create a resource that was created on a different event loop, for example asyncio.Tasks and a global aiohttp.ClientSession object. It also looks like Vercel makes every new request go through the sync function vc_handler(). So we run an event loop on a separate thread and make all requests use that one loop.

2. Runs the __aenter__ part of lifespan.

Vercel does not support lifespan. Lifespan is used init async code, like creating a database connection pool. This runs once per instance, not per request, so whatever is in there contributes to the coldstart time. A reference is kept so the Garbage Collector won't silently raise GeneratorExit on it. Finally, this only supports Starlette's lifespan which located in app.router.lifespan_context. This part will be skipped if no lifespan was found.

In your vercel.json file, change the npm package to use to @imptype/[email protected], for example:

{
  "builds": [
    {
      "src": "main.py",
      "use": "@imptype/[email protected]"
    }
  ],
  "routes": [
    {
      "src": "/(.*)",
      "dest": "main.py"
    }
  ]
}

• 3.4.12 - Uses shared event loop
• 3.4.35 - Uses shared event loop and runs the __aenter__ part of lifespan