fix(Plugs.RecentlyVisited): handle task timeout

[thecristen]

Scope

(from the homepage) MBTA-DOTCOM-JN
(from the mode pages, e.g. /schedules/bus) MBTA-DOTCOM-JM

Uncaught exit - {:timeout, {Task.Supervised, :stream, [5000]}}
    lib/task/supervised.ex:349: Elixir.Task.Supervised.Task.Supervised.stream_reduce/7
    lib/enum.ex:4570: Elixir.Enum.Enum.reduce/3
    lib/dotcom_web/plugs/recently_visited.ex:33: Elixir.DotcomWeb.Plugs.RecentlyVisited.DotcomWeb.Plugs.RecentlyVisited.assign_recently_visited/2
    lib/dotcom_web/controllers/mode_controller.ex:1: Elixir.DotcomWeb.ModeController.DotcomWeb.ModeController.phoenix_controller_pipeline/2
    lib/phoenix/router.ex:416: Elixir.Phoenix.Router.Phoenix.Router.__call__/5
    deps/plug/lib/plug/error_handler.ex:80: Elixir.DotcomWeb.Router.DotcomWeb.Router.call/2
    lib/dotcom_web/endpoint.ex:1: Elixir.DotcomWeb.Endpoint.DotcomWeb.Endpoint.plug_builder_call/2
    lib/dotcom_web/endpoint.ex:1: Elixir.DotcomWeb.Endpoint.DotcomWeb.Endpoint."call (overridable 3)"/2

Implementation

The Task.async_stream/3 call wasn't handling the timeout! So now we can handle the timeout, by specifying on_timeout. (We don't do anything special with the result - if we can't fetch the route we'll ignore it.)

I also adjusted the call in the ModeController: it turns out we were calling the plug on each mode, but we don't even show Recently Visited routes on those pages. So now it's only run on the /schedules/ page.

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[thecristen]

Updated with another commit (refactor(Plugs.RecentlyVisited): use Stream) which tackles 📈 Speed up Recently-Visited call on the homepage

edit: forgot the flamegraphs

Before	After