class Sidekiq::ProcessSet

def cleanup
  # dont run cleanup more than once per minute
  return 0 unless Sidekiq.redis { |conn| conn.set("process_cleanup", "1", "NX", "EX", "60") }
  count = 0
  Sidekiq.redis do |conn|
    procs = conn.sscan("processes").to_a
    heartbeats = conn.pipelined { |pipeline|
      procs.each do |key|
        pipeline.hget(key, "info")
      end
    }
    # the hash named key has an expiry of 60 seconds.
    # if it's not found, that means the process has not reported
    # in to Redis and probably died.
    to_prune = procs.select.with_index { |proc, i|
      heartbeats[i].nil?
    }
    count = conn.srem("processes", to_prune) unless to_prune.empty?
  end
  count
end