Class: ZK::Election::Observer

Inherits:
Base
  • Object
show all
Defined in:
lib/z_k/election.rb

Instance Attribute Summary

Attributes inherited from Base

#root_election_node, #vote_path, #zk

Instance Method Summary collapse

Methods inherited from Base

#cast_ballot!, #create_root_path!, #digit, #leader_ack_path, #leader_acked?, #leader_data, #on_leader_ack, #root_vote_path, #safe_call, #vote_basename

Constructor Details

#initialize(client, name, opts = {}) ⇒ Observer

Returns a new instance of Observer.



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# File 'lib/z_k/election.rb', line 319

def initialize(client, name, opts={})
  super
  @leader_death_cbs = []
  @new_leader_cbs = []
  @deletion_sub = @creation_sub = nil
  @leader_alive = nil
  @observing = false
end

Instance Method Details

#close ⇒ Object 



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# File 'lib/z_k/election.rb', line 377

def close
  @mutex.synchronize do
    return unless @observing

    @deletion_sub.unregister if @deletion_sub
    @creation_sub.unregister if @creation_sub

    @deletion_sub = @creation_sub = nil

    @leader_death_cbs.clear
    @new_leader_cbs.clear

    @leader_alive = nil
    @observing = false
  end
end

#leader_alive ⇒ Object

our current idea about the state of the election



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# File 'lib/z_k/election.rb', line 329

def leader_alive #:nodoc:
  @mutex.synchronize { @leader_alive }
end

#long_live_the_king ⇒ Object (protected) 



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# File 'lib/z_k/election.rb', line 404

def long_live_the_king
  @mutex.synchronize do
    safe_call(*@new_leader_cbs)
    @leader_alive = true
  end

  the_king_is_dead unless leader_acked?(true)
end

#observe! ⇒ Object 



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# File 'lib/z_k/election.rb', line 344

def observe!
  @mutex.synchronize do
    return if @observing 
    @observing = true

    @leader_ack_sub ||= @zk.watcher.register(leader_ack_path) do |event|
      logger.debug { "leader_ack_callback, event.node_deleted? #{event.node_deleted?}, event.node_created? #{event.node_created?}" }

      if event.node_deleted?
        the_king_is_dead 
      elsif event.node_created?
        long_live_the_king
      else
        acked = leader_acked?(true) 


        # If the current state of the system is not what we think it should be
        # a transition has occurred and we should fire our callbacks
        if (acked and !@leader_alive)
          long_live_the_king 
        elsif (!acked and @leader_alive)
          the_king_is_dead
        else
          # things are how we think they should be, so just wait for the
          # watch to fire
        end
      end
    end

    leader_acked?(true) ? long_live_the_king : the_king_is_dead
  end
end

#on_leaders_death(&blk) ⇒ Object

register callbacks that should be fired when a leader dies



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# File 'lib/z_k/election.rb', line 334

def on_leaders_death(&blk)
  @leader_death_cbs << blk
end

#on_new_leader(&blk) ⇒ Object

register callbacks for when the new leader has acknowledged their role returns a subscription object that can be used to cancel further events



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# File 'lib/z_k/election.rb', line 340

def on_new_leader(&blk)
  @new_leader_cbs << blk
end

#the_king_is_dead ⇒ Object (protected) 



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# File 'lib/z_k/election.rb', line 395

def the_king_is_dead
  @mutex.synchronize do
    safe_call(*@leader_death_cbs)
    @leader_alive = false
  end

  long_live_the_king if leader_acked?(true)
end