Endpoint: race condition with warmup/1

[paulswartz]

Environment

• Elixir version (elixir -v): 1.17.3
• Phoenix version (mix deps): 1.7.14
• Operating system: Debian bookworm

Actual behavior

It appears that there's a race condition when starting the endpoint:

8ac841655ae8 01:33:12.681 [info] Running RideAlongWeb.Endpoint with Bandit 1.6.0 at :::4000 (http)
8ac841655ae8 01:33:12.685 [error] ** (RuntimeError) could not find persistent term for endpoint RideAlongWeb.Endpoint. Make sure your endpoint is started and note you cannot access endpoint functions at compile-time
8ac841655ae8     (ride_along 0.1.0) deps/phoenix/lib/phoenix/endpoint.ex:544: RideAlongWeb.Endpoint.persistent!/0
8ac841655ae8     (ride_along 0.1.0) deps/phoenix/lib/phoenix/endpoint.ex:584: RideAlongWeb.Endpoint.script_name/0
8ac841655ae8     (ride_along 0.1.0) lib/ride_along_web/endpoint.ex:1: RideAlongWeb.Endpoint.call/2
8ac841655ae8     (bandit 1.6.0) lib/bandit/pipeline.ex:127: Bandit.Pipeline.call_plug!/2
8ac841655ae8     (bandit 1.6.0) lib/bandit/pipeline.ex:36: Bandit.Pipeline.run/4
8ac841655ae8     (bandit 1.6.0) lib/bandit/http1/handler.ex:12: Bandit.HTTP1.Handler.handle_data/3
8ac841655ae8     (bandit 1.6.0) lib/bandit/delegating_handler.ex:18: Bandit.DelegatingHandler.handle_data/3
8ac841655ae8     (bandit 1.6.0) /app/deps/thousand_island/lib/thousand_island/handler.ex:417: Bandit.DelegatingHandler.handle_continue/2
8ac841655ae8 01:33:12.685 [info] Access RideAlongWeb.Endpoint at XXX

I think this is the relevant code in Phoenix.Endpoint.Supervisor:

phoenix/lib/phoenix/endpoint/supervisor.ex

Lines 13 to 16 in 222d9ab

	with {:ok, pid} = ok <- Supervisor.start_link(__MODULE__, {otp_app, mod, opts}, name: mod) do
	# We don't use the defaults in the checks below
	conf = Keyword.merge(Application.get_env(otp_app, mod, []), opts)
	warmup(mod)

The call to warmup/1 (which sets the persistent term) happens after the Endpoint is started, so there's a small window where the HTTP server is accepting connections, but the underlying data has not been set up.

Expected behavior

All the underlying data is available when the server is accepting connections.