Module: Politics::StaticQueueWorker

Defined in:
lib/politics/static_queue_worker.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#buckets ⇒ Object (readonly)

Returns the value of attribute buckets.



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# File 'lib/politics/static_queue_worker.rb', line 18

def buckets
  @buckets
end

#dictatorship_length ⇒ Object (readonly)

Returns the value of attribute dictatorship_length.



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# File 'lib/politics/static_queue_worker.rb', line 18

def dictatorship_length
  @dictatorship_length
end

#group_name ⇒ Object (readonly)

Returns the value of attribute group_name.



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# File 'lib/politics/static_queue_worker.rb', line 18

def group_name
  @group_name
end

#iteration_length ⇒ Object (readonly)

Returns the value of attribute iteration_length.



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# File 'lib/politics/static_queue_worker.rb', line 18

def iteration_length
  @iteration_length
end

#uri ⇒ Object (readonly)

Returns the value of attribute uri.



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# File 'lib/politics/static_queue_worker.rb', line 18

def uri
  @uri
end

Instance Method Details

#alive? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/politics/static_queue_worker.rb', line 155

def alive?
  true
end

#as_dictator(&block) ⇒ Object 



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# File 'lib/politics/static_queue_worker.rb', line 81

def as_dictator(&block)
  duration = dictatorship_length || (iteration_length * 10)
  log.debug { "become dictator for up to #{duration} seconds" }
  seize_leadership duration
  yield
  raise "lost leadership while being dictator for #{duration} seconds" unless leader?
  seize_leadership
end

#bucket_request(requestor_uri) ⇒ Object 



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# File 'lib/politics/static_queue_worker.rb', line 127

def bucket_request(requestor_uri)
  if leader?
    log.debug "delivering bucket request"
    bucket_spec = next_bucket(requestor_uri)
    if !bucket_spec[0] && @followers_to_stop.include?(requestor_uri)
      bucket_spec = [:stop, 0]
      @followers_to_stop.delete(requestor_uri)
    end
    bucket_spec
  else
    log.debug "received request for bucket but am not leader - delivering :not_leader"
    [:not_leader, 0]
  end
end

#find_workers ⇒ Object 



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# File 'lib/politics/static_queue_worker.rb', line 169

def find_workers
  raise "Please provide a method ”find_workers” returning a list of all other worker URIs"
end

#followers_to_stop ⇒ Object 



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# File 'lib/politics/static_queue_worker.rb', line 123

def followers_to_stop
  @followers_to_stop.select {|u| DRbObject.new(nil, u).alive? rescue DRb::DRbConnError && false}
end

#leader ⇒ Object 



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# File 'lib/politics/static_queue_worker.rb', line 159

def leader
  2.times do
    break if leader_uri
    log.debug "could not determine leader - relaxing until next iteration"
    relax until_next_iteration
  end
  raise "cannot determine leader" unless leader_uri
  DRbObject.new(nil, leader_uri)
end

#next_bucket(requestor_uri) ⇒ Object 



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# File 'lib/politics/static_queue_worker.rb', line 142

def next_bucket(requestor_uri)
  [@buckets.pop, sleep_until_next_bucket_time]
end

#perform_leader_duties ⇒ Object 



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# File 'lib/politics/static_queue_worker.rb', line 95

def perform_leader_duties
  # Drb thread handles requests to leader
  as_dictator do
    initialize_buckets
  end
  # keeping leader state as long as buckets are available by renominating before nomination
  # times out
  while !buckets.empty? do
    log.debug { "relaxes half the time until next iteration" }
    relax(until_next_iteration / 2)
    as_dictator do
      update_buckets unless restart_wanted?
    end
  end
  as_dictator() {populate_followers_to_stop} if restart_wanted?
  # keeping leader state as long as there are followers to stop
  while !followers_to_stop.empty? do
    relax(until_next_iteration / 2)
    seize_leadership
  end
  exit 0 if restart_wanted?
  relax until_next_iteration
end

#populate_followers_to_stop ⇒ Object 



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# File 'lib/politics/static_queue_worker.rb', line 119

def populate_followers_to_stop
  @followers_to_stop.replace(find_workers)
end

#process_bucket(&block) ⇒ Object

Fetch a bucket out of the queue and pass it to the given block to be processed.

Raises:

  • (ArgumentError) 


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# File 'lib/politics/static_queue_worker.rb', line 46

def process_bucket(&block)
  log.debug "start bucket processing"
  raise ArgumentError, "process_bucket requires a block!" unless block_given?
  unless @memcache_client
    raise ArgumentError, "You must call register_worker before processing!"
  end

  begin
    begin
      raise "self is not alive via drb" unless DRbObject.new(nil, uri).alive?
    rescue Exception => e
      raise "cannot reach self via drb: #{e.message}"
    end
    begin
      nominate
      if leader?
        log.info { "has been elected leader" }
        perform_leader_duties
      else
        # Get a bucket from the leader and process it
        begin
          log.debug "getting bucket request from leader (#{leader_uri}) and processing it"
          bucket_process(*leader.bucket_request(uri), &block)
        rescue DRb::DRbError => dre
          log.error { "Error talking to leader: #{dre.message}" }
          relax until_next_iteration
        end
      end
    rescue MemCache::MemCacheError => e
      log.error { "Unexpected MemCacheError: #{e.message}" }
      relax until_next_iteration
    end
  end while loop?
end

#register_worker(name, bucket_count, config = {}) ⇒ Object

Register this process as able to work on buckets.



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# File 'lib/politics/static_queue_worker.rb', line 21

def register_worker(name, bucket_count, config = {})
  options = {
        :iteration_length => 10,
        :servers => ['127.0.0.1:11211']
      }.merge(config)

  @group_name = name
  @iteration_length = options[:iteration_length]
  @memcache_client = client_for(Array(options[:servers]))
  @nominated_at = Time.now
  @dictatorship_length = options[:dictatorship_length]

  @buckets = []
  @bucket_count = bucket_count
  @followers_to_stop = Set.new

  start_druby_service
  log.progname = uri
  log.info { "Registered in group #{group_name} at #{uri}" }
  at_exit do
    cleanup
  end
end

#seize_leadership(duration = iteration_length) ⇒ Object 



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# File 'lib/politics/static_queue_worker.rb', line 90

def seize_leadership(duration = iteration_length)
  @memcache_client.set(token, uri, duration)
  @nominated_at = Time.now + duration - iteration_length
end

#sleep_until_next_bucket_time ⇒ Object 



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# File 'lib/politics/static_queue_worker.rb', line 146

def sleep_until_next_bucket_time
  [[until_next_iteration / 2, 1].max, iteration_length / 2].min
end

#until_next_iteration ⇒ Object 



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# File 'lib/politics/static_queue_worker.rb', line 150

def until_next_iteration
  left = iteration_length - (Time.now - @nominated_at)
  left > 0 ? left : 0
end