Presence for Rails Action Cable
Presence is the "3 people are viewing this" list: who has the page open right now.
The Action Cable guide's pattern adds you on subscribed and removes you on
unsubscribed, so when a server process dies or a laptop lid closes, that callback
never runs and you stay listed forever as a ghost.
actioncable-presence owns every row by a leased process, so a killed worker's users
leave within about 10 seconds, and a silent client is dropped within about 9.
You'll be Cosmic vole. Share the room link with a friend, or open it in a second browser.
One button sends kill -9 to the Puma worker holding your WebSocket. No callbacks run.
Puma respawns the worker, you reconnect, and your old connection's row is a ghost. A countdown shows when it clears.
Next to it, the same room tracked the guide's way: insert on subscribe, delete on unsubscribe. After the kill, that list keeps your ghost until someone presses Reset.
"Simulate a dead network" stops your tab answering pings, like a closed laptop lid. The server notices within 9 seconds and everyone else sees you leave.
One concern on the channel. The client is a small reconciler with a React hook, or plain JS like this page uses.
class RoomChannel < ApplicationCable::Channel
include ActionCable::Presence::Channel
def subscribed
stream_from "room:#{params[:id]}"
join_presence(id: current_user.id, info: { name: current_user.name })
end
end