Unsubscription impossible because #subscribe blocks

[paddor]

Due to the blocking nature of Redis#subscribe, I think it's pretty much impossible to unsubscribe from a subscription channel (except maybe from a subscription callback). Have a look at this code:

require 'celluloid'
require 'celluloid/redis'

class RedisListener
  include Celluloid
  include Celluloid::Logger

  CHANNEL = "updates"

  def initialize(redis)
    @redis = redis
    async.subscribe
  end

  # Subscribes to the channel on and forwards messages them via
  # the broker actor.
  def subscribe
    info "Subscribing to Redis channel #{CHANNEL.inspect} ..."
    @redis.subscribe(CHANNEL) do |on|
      on.message do |channel,msg|
        info "Received message from Redis: #{msg.inspect}"
        Actor[:broker].forward(msg)
      end
    end
  end

  def unsubscribe
    info "unsubscribing from Redis ..."
    @redis.unsubscribe(CHANNEL)
  end
  finalizer :unsubscribe
end

class Broker
  include Celluloid
  include Celluloid::Logger

  def forward(msg)
    info "Forwarding message #{msg.inspect}"
  end
end


Celluloid.register_shutdown

Broker.supervise_as :broker
redis = Redis.new(driver: :celluloid)
RedisListener.supervise_as :redis_listener, redis

warn "sleeping in main thread"
sleep

It starts fine and even prints the "sleeping in main thread" message (which it wouldn't if the call to #subscribe wasn't async. When I hit Ctrl-C to stop the program it tries to terminate the actors cleanly but fails.

I, [2014-09-24T22:43:25.555864 #80670]  INFO -- : Subscribing to Redis channel "updates" ...
sleeping in main thread
^CD, [2014-09-24T22:43:28.035428 #80670] DEBUG -- : Terminating 4 actors...
E, [2014-09-24T22:43:38.036333 #80670] ERROR -- : Couldn't cleanly terminate all actors in 10 seconds!
celluloid-redis.report.rb:51:in `sleep': Interrupt
    from celluloid-redis.report.rb:51:in `<main>'

What's the right way to unsubscribe and cleanly shutdown this actor?

[jduarte]

I'm having this exact same issue.
Do you know any way to solve this?

@chriseppstein had this issue as well https://twitter.com/chriseppstein/status/275690390185717762

[tarcieri]

Has anyone looked into whether the monkeypatch this gem implements still actually works? If it does, this should be fine.

[paddor]

Any updates on this? Should I close this issue?

Back then, I switched from pub/sub to a simple Redis queue (LPUSH/BRPOP).