huginn/app/jobs/agent_propagate_job.rb

class AgentPropagateJob < ActiveJob::Base
  queue_as :propagation

  def perform
    Agent.receive!
  end

  def self.can_enqueue?
    case queue_adapter.class.name # not using class since it would load adapter dependent gems
    when 'ActiveJob::QueueAdapters::DelayedJobAdapter'
      return Delayed::Job.where(failed_at: nil, queue: 'propagation').count == 0
    when 'ActiveJob::QueueAdapters::ResqueAdapter'
      return Resque.size('propagation') == 0 &&
             Resque.workers.select { |w| w.job && w.job['queue'] && w.job['queue']['propagation'] }.count == 0
    else
      raise NotImplementedError, "unsupported adapter: #{queue_adapter}"
    end
  end

end