module CloudCrowd

  # The dispatcher is responsible for distributing work_units
  # to the worker nodes.
  #
  # It automatically performs the distribution on a set schedule,
  # but can also be signaled to perform distribution immediately
  class Dispatcher

    # Starts distributing jobs every "distribution_interval" seconds
    def initialize(distribution_interval)
      @mutex  = Mutex.new
      @awaken = ConditionVariable.new
      distribute_periodically(distribution_interval)
    end

    # Sends a signal to the distribution thread.
    # If it's asleep, it will wake up and perform a distribution.
    def distribute!
      @mutex.synchronize do
        @awaken.signal
      end
    end

    private

    # Perform distribution of work units in a background thread
    def distribute_periodically(interval)
      Thread.new{
        loop do
          perform_distribution
          # Sleep for "interval" seconds.
          # If awaken isn't signaled, timeout and attempt distribution
          @mutex.synchronize do
            @awaken.wait(@mutex, interval)
          end
        end
      }
    end

    def perform_distribution
      #CloudCrowd.log "Distributing jobs to nodes"
      begin
        WorkUnit.distribute_to_nodes
      rescue StandardError => e
        CloudCrowd.log "Exception: #{e}"
        CloudCrowd.log e.backtrace
      end
    end

  end
end