Add loop_factory parameter for persistent event loops

[jrobbins-LiveData]

Summary

Adds an optional loop_factory parameter to Mangum that enables persistent event loops across Lambda invocations. This is similar to uvicorn's loop parameter.

Use cases:

• Reusing async resources (database connections, HTTP clients) across warm invocations
• Using alternative event loop implementations like uvloop for better performance
• Managing the event loop externally for advanced lifecycle control

Changes

• Added loop_factory: LoopFactory | None parameter to Mangum.__init__
• When provided, the factory is called once at initialization and the loop is reused for all invocations
• Added LoopFactory type alias to mangum.types for external use
• Added documentation section "Persistent event loop" to docs/adapter.md
• Added 4 tests covering the new functionality

Usage

import asyncio
from mangum import Mangum

handler = Mangum(app, lifespan="off", loop_factory=asyncio.new_event_loop)

Or with uvloop:

import uvloop
from mangum import Mangum

handler = Mangum(app, lifespan="off", loop_factory=uvloop.new_event_loop)

Notes

The loop is not closed automatically by Mangum - in Lambda, it persists until the execution environment is recycled
For testing, callers are responsible for closing the loop explicitly

Related

Addresses use case discussed in #361

[Kludex]

asyncio_run receives loop_factory already, the idea was to pass that, wasn't it?

[jrobbins-LiveData]

AFAICT, passing loop_factory to asyncio_run() would still create and close a new loop per Lambda invocation, which would defeat the intent to keep the same event loop instance alive across Lambda invocations so that async resources (database connection pools, HTTP client sessions, etc) persist in warm containers. The run_until_complete() approach reuses the same loop instance.

[tampueroc]

Hi @jrobbins-LiveData. Is the issue still persisting after #375?

[jrobbins-LiveData]

@tampueroc, the revert to previous loop behavior in #376 fixed the issue that #375 had caused us.