Prioritised queue consumption with multiple queues

consumption.rb

queues = []
queues << queue_consumer("high")
queues << queue_consumer("normal")

def next_message
  # look for a message from each queue in priority order
  queues.each do |queue|
    found, message = queue.non_blocking_dequeue
    return [found, message] if found
  end

  # block on the highest priority queue for a while to avoid pounding
  # what is a sensible time depends on your case
  queues.first.blocking_dequeue(500ms)
end

while true do # make this a changeable flag to stop consuming gracefully
  found, message = next_message

  if found
    process_message(message)
    ack_message(message)
  end
end

Another thought, if contention isn't your reason for prioritising (so you can have multiple consumers), you need to be careful of the prefetch configuration. Otherwise one consumer can prefetch all the "high" tasks whilst all the others work on the remaining "low" tasks.