neiam /apollos_crib

It's Apollo's Crib

Tell an empty answer apart from no answer

4758a10 · Gabriel Morell · 2026-09-02 19:11

10 files +55 -5

Message

{commit_body(@commit)}

modified apps/room_sanctum/lib/room_sanctum/storage.ex

+6 −1

@@ -1617,7 +1617,12 @@ defmodule RoomSanctum.Storage do

1617	1617	tz: ^tz
1618	1618	}
1619	1619	)
1620		− \|> Repo.all()
	1620	+ # Ecto's default of 15s was cancelling arrival lookups that the caller was
	1621	+ # perfectly willing to wait for -- the vision allows a query 25s -- and a
	1622	+ # cancelled statement raises, which used to publish "nothing is coming" on
	1623	+ # the strength of a timeout. The layers now agree; the lookups being this
	1624	+ # slow at all is a separate problem.
	1625	+ \|> Repo.all(timeout: 20_000)
1621	1626
1622	1627	# q =
1623	1628	# from st in StopTime,

modified apps/room_sanctum/lib/room_sanctum/workers/vision_worker.ex

+14 −4

@@ -276,27 +276,37 @@ defmodule RoomSanctum.Worker.Vision do

276	276	# was slow or broken, and is why waiting would be the wrong move.
277	277	defp query_cached(q) do
278	278	case RoomSanctum.QueryCache.fetch({q.id, q.source.type}, fn -> query_safely(q) end) do
279		− {:ok, result} -> {:ok, result}
	279	+ # query_safely already tags its own outcome, so this is {:ok, {:ok, _}}
	280	+ # or {:ok, :skip} -- the cache does not care which it is holding.
	281	+ {:ok, outcome} -> outcome
280	282	:busy -> :skip
281	283	end
282	284	end
283	285
	286	+ # `:skip` rather than an empty list, and the difference matters.
	287	+ #
	288	+ # An empty list is a real answer -- nothing calls at this stop in the next
	289	+ # hour -- and writing it is correct. A query that raised has no answer at
	290	+ # all, and returning [] for it published "nothing is coming" on the strength
	291	+ # of a database timeout. The panel blanked, which is the very thing keeping
	292	+ # the last value was meant to prevent; it just arrived by a different route
	293	+ # than a task being killed.
284	294	defp query_safely(q) do
285		− query_one(q)
	295	+ {:ok, query_one(q)}
286	296	rescue
287	297	e ->
288	298	Logger.warning(
289	299	"Query failed for #{inspect(q.source.type)} (#{q.source.id}): #{Exception.message(e)}"
290	300	)
291	301
292		− []
	302	+ :skip
293	303	catch
294	304	kind, reason ->
295	305	Logger.warning(
296	306	"Query #{kind} for #{inspect(q.source.type)} (#{q.source.id}): #{inspect(reason)}"
297	307	)
298	308
299		− []
	309	+ :skip
300	310	end
301	311
302	312	defp query_one(q) do

modified apps/room_sanctum/test/room_sanctum/vision_merge_test.exs

+35 −0

@@ -192,6 +192,41 @@ defmodule RoomSanctum.VisionMergeTest do

192	192	end
193	193	end
194	194
	195	+ describe "an empty answer versus no answer" do
	196	+ test "a genuinely empty result is written" do
	197	+ {ref, entry} = outstanding(@key)
	198	+
	199	+ s0 = state(%{data: %{@key => [:yesterday]}, inflight: %{ref => entry}})
	200	+ {:noreply, s} = Vision.handle_info({ref, {:ok, []}}, s0)
	201	+
	202	+ # Nothing calls at this stop in the next hour is a real answer.
	203	+ assert s.data[@key] == []
	204	+ end
	205	+
	206	+ test "a query that raised keeps what it had" do
	207	+ {ref, entry} = outstanding(@key)
	208	+
	209	+ s0 = state(%{data: %{@key => [:yesterday]}, inflight: %{ref => entry}})
	210	+ {:noreply, s} = Vision.handle_info({ref, :skip}, s0)
	211	+
	212	+ # Returning [] here published "nothing is coming" on the strength of a
	213	+ # database timeout.
	214	+ assert s.data[@key] == [:yesterday]
	215	+ assert s.inflight == %{}
	216	+ end
	217	+
	218	+ test "a skip does not move the timestamp either" do
	219	+ {ref, entry} = outstanding(@key)
	220	+ at = %{@key => ~U[2026-09-01 00:00:00Z]}
	221	+
	222	+ s0 = state(%{data: %{@key => [:a]}, data_at: at, inflight: %{ref => entry}})
	223	+ {:noreply, s} = Vision.handle_info({ref, :skip}, s0)
	224	+
	225	+ # The panel is as old as its data actually is.
	226	+ assert s.data_at[@key] == ~U[2026-09-01 00:00:00Z]
	227	+ end
	228	+ end
	229	+
195	230	describe "state given out" do
196	231	test "carries when each answer arrived" do
197	232	at = %{@key => ~U[2026-09-01 12:00:00Z]}

Parents: 04f2bcb