Class: ZK::Election::Base

Inherits:
Object
  • Object
show all
Includes:
Logging
Defined in:
lib/zk/election.rb

Direct Known Subclasses

Candidate, Observer

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

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

Returns a new instance of Base.



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# File 'lib/zk/election.rb', line 69

def initialize(client, name, opts={})
  @zk = client
  @name = name
  opts = DEFAULT_OPTS.merge(opts)
  @root_election_node = opts[:root_election_node]
  @mutex = Monitor.new
end

Instance Attribute Details

#root_election_node ⇒ Object (readonly)

Returns the value of attribute root_election_node.



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# File 'lib/zk/election.rb', line 67

def root_election_node
  @root_election_node
end

#vote_path ⇒ Object (readonly)

Returns the value of attribute vote_path.



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# File 'lib/zk/election.rb', line 67

def vote_path
  @vote_path
end

#zk ⇒ Object (readonly)

Returns the value of attribute zk.



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# File 'lib/zk/election.rb', line 67

def zk
  @zk
end

Instance Method Details

#cast_ballot!(data) ⇒ Object 



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# File 'lib/zk/election.rb', line 89

def cast_ballot!(data)
  return if @vote_path
  create_root_path!
  @vote_path = @zk.create("#{root_vote_path}/#{VOTE_PREFIX}", data, :mode => :ephemeral_sequential)
rescue Exceptions::NoNode
  retry
end

#create_root_path! ⇒ Object (protected) 



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# File 'lib/zk/election.rb', line 146

def create_root_path!
  @zk.mkdir_p(root_vote_path)
end

#digit(path) ⇒ Object (protected) 



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# File 'lib/zk/election.rb', line 154

def digit(path)
  path[/\d+$/].to_i
end

#leader_ack_path ⇒ Object

this znode will be created as an acknowledgement by the leader that it's aware of its status as the new leader and has run its procedures to become master



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# File 'lib/zk/election.rb', line 85

def leader_ack_path
  @leader_ack_path ||= "#{root_vote_path}/leader_ack"
end

#leader_acked?(watch = false) ⇒ Boolean

has the leader acknowledged their role?

Returns:

  • (Boolean) 


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# File 'lib/zk/election.rb', line 98

def leader_acked?(watch=false)
  @zk.exists?(leader_ack_path, :watch => watch)
end

#leader_data ⇒ Object

return the data from the current leader or nil if there is no current leader



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# File 'lib/zk/election.rb', line 103

def leader_data
  @zk.get(leader_ack_path).first
rescue Exceptions::NoNode
end

#on_leader_ack(&block) ⇒ Object

Asynchronously call the block when the leader has acknowledged its role.



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# File 'lib/zk/election.rb', line 110

def on_leader_ack(&block)
  creation_sub = @zk.register(leader_ack_path, :only => [:created, :changed]) do |event|
    begin
      logger.debug { "in #{leader_ack_path} watcher, got creation event, notifying" }
      safe_call(block)
    ensure
      creation_sub.unregister
    end
  end

  deletion_sub = @zk.register(leader_ack_path, :only => [:deleted, :child]) do |event|
    if @zk.exists?(leader_ack_path, :watch => true)
      begin
        logger.debug { "in #{leader_ack_path} watcher, node created behind our back, notifying" }
        safe_call(block)
      ensure
        creation_sub.unregister
      end
    else
      logger.debug { "in #{leader_ack_path} watcher, got non-creation event, re-watching" }
    end
  end

  subs = [creation_sub, deletion_sub]

  if @zk.exists?(leader_ack_path, :watch => true)
    logger.debug { "on_leader_ack, #{leader_ack_path} exists, calling block" }
    begin
      safe_call(block)
    ensure
      subs.each { |s| s.unregister }
    end
  end
end

#root_vote_path ⇒ Object

holds the ephemeral nodes of this election



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# File 'lib/zk/election.rb', line 78

def root_vote_path #:nodoc:
  @root_vote_path ||= "#{@root_election_node}/#{@name.gsub('/', '__')}"
end

#safe_call(*callbacks) ⇒ Object (protected) 



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# File 'lib/zk/election.rb', line 158

def safe_call(*callbacks)
  callbacks.each do |cb|
    begin
      cb.call
    rescue Exception => e
      logger.error { "Error caught in user supplied callback" }
      logger.error { e.to_std_format }
    end
  end
end

#synchronize ⇒ Object (protected) 



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# File 'lib/zk/election.rb', line 169

def synchronize
#           call_line = caller[0..-2]
#           logger.debug { "synchronizing, backtrace:\n#{call_line.join("\n")}" }
  @mutex.synchronize { yield }
end

#vote_basename ⇒ Object (protected) 



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# File 'lib/zk/election.rb', line 150

def vote_basename
  vote_path and File.basename(vote_path)
end