Redis + ActionController::Live threads not dying

Question

Background: We\'ve built a chat feature in to one of our existing Rails applications. We\'re using the new ActionController::Live module and ru

Answer 1

Here you are solution with timeout that will exit blocking Redis.(p)subscribe call and kill unused connection tread.

class Stream::FixedController < StreamController
  def events
    # Rails reserve a db connection from connection pool for
    # each request, lets put it back into connection pool.
    ActiveRecord::Base.clear_active_connections!

    # Last time of any (except heartbeat) activity on stream
    # it mean last time of any message was send from server to client
    # or time of setting new connection
    @last_active = Time.zone.now

    # Redis (p)subscribe is blocking request so we need do some trick
    # to prevent it freeze request forever.
    redis.psubscribe("messages:*", 'heartbeat') do |on|
      on.pmessage do |pattern, event, data|
        # capture heartbeat from Redis pub/sub
        if event == 'heartbeat'
          # calculate idle time (in secounds) for this stream connection
          idle_time = (Time.zone.now - @last_active).to_i

          # Now we need to relase connection with Redis.(p)subscribe
          # chanel to allow go of any Exception (like connection closed)
          if idle_time > 4.minutes
            # unsubscribe from Redis because of idle time was to long
            # that's all - fix in (almost)one line :)
            redis.punsubscribe
          end
        else
          # save time of this (last) activity
          @last_active = Time.zone.now
        end
        # write to stream - even heartbeat - it's sometimes chance to
        # capture dissconection error before idle_time
        response.stream.write("event: #{event}\ndata: #{data}\n\n")
      end
    end
    # blicking end (no chance to get below this line without unsubscribe)
  rescue IOError
    Logs::Stream.info "Stream closed"
  rescue ClientDisconnected
    Logs::Stream.info "ClientDisconnected"
  rescue ActionController::Live::ClientDisconnected
    Logs::Stream.info "Live::ClientDisconnected"
  ensure
    Logs::Stream.info "Stream ensure close"
    redis.quit
    response.stream.close
  end
end

You have to use reds.(p)unsubscribe to end this blocking call. No exception can break this.

My simple app with information about this fix: https://github.com/piotr-kedziak/redis-subscribe-stream-puma-fix