Class: ZK::EventHandler

Inherits:
Object
  • Object
show all
Includes:
Logging
Defined in:
lib/z_k/event_handler.rb

Overview

this is the default watcher provided by the zookeeper connection watchers are implemented by adding the :watch => true flag to any #children or #get or #exists calls you never really need to initialize this yourself

Constant Summary collapse

VALID_WATCH_TYPES = 
[:data, :child].freeze
ZOOKEEPER_WATCH_TYPE_MAP = 
{
  Zookeeper::ZOO_CREATED_EVENT => :data,
  Zookeeper::ZOO_DELETED_EVENT => :data,
  Zookeeper::ZOO_CHANGED_EVENT => :data,
  Zookeeper::ZOO_CHILD_EVENT   => :child,
}.freeze

Instance Attribute Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#zk ⇒ Object

:nodoc:



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# File 'lib/z_k/event_handler.rb', line 19

def zk
  @zk
end

Instance Method Details

#clear! ⇒ Object

used during shutdown to clear registered listeners



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# File 'lib/z_k/event_handler.rb', line 130

def clear! #:nodoc:
  synchronize do
    @callbacks.clear
    nil
  end
end

#get_default_watcher_block ⇒ Object 



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# File 'lib/z_k/event_handler.rb', line 141

def get_default_watcher_block
  @default_watcher_block ||= lambda do |hash|
    watcher_callback.tap do |cb|
      cb.call(hash)
    end
  end
end

#process(event) ⇒ Object

called from the client-registered callback when an event fires



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# File 'lib/z_k/event_handler.rb', line 96

def process(event) #:nodoc:
#       logger.debug { "EventHandler#process dispatching event: #{event.inspect}" }# unless event.type == -1
  event.zk = @zk

  cb_key = 
    if event.node_event?
      event.path
    elsif event.state_event?
      state_key(event.state)
    else
      raise ZKError, "don't know how to process event: #{event.inspect}"
    end

#       logger.debug { "EventHandler#process: cb_key: #{cb_key}" }

  cb_ary = synchronize do 
    if event.node_event?
      if watch_type = ZOOKEEPER_WATCH_TYPE_MAP[event.type]
#             logger.debug { "re-allowing #{watch_type.inspect} watches on path #{event.path.inspect}" }
        
        # we recieved a watch event for this path, now we allow code to set new watchers
        @outstanding_watches[watch_type].delete(event.path)
      end
    end

    @callbacks[cb_key].dup
  end

  cb_ary.compact!

  safe_call(cb_ary, event)
end

#register(path, &block) {|connection, event| ... } ⇒ ZooKeeper::EventHandlerSubscription Also known as: subscribe

register a path with the handler your block will be called with all events on that path. aliased as #subscribe

Parameters:

  • path (String) —

    the path you want to listen to

  • block (Block) —

    the block to execute when a watch event happpens

Yields:

  • (connection, event) —

    We will call your block with the connection the watch event occured on and the event object

Returns:

  • (ZooKeeper::EventHandlerSubscription) —

    the subscription object you can use to to unsubscribe from an event

See Also:

  • ZooKeeper::WatcherEvent
  • ZooKeeper::EventHandlerSubscription


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# File 'lib/z_k/event_handler.rb', line 45

def register(path, &block)
#       logger.debug { "EventHandler#register path=#{path.inspect}" }
  EventHandlerSubscription.new(self, path, block).tap do |subscription|
    synchronize { @callbacks[path] << subscription }
  end
end

#register_state_handler(state, &block) {|connection, event| ... } ⇒ Object

registers a “state of the connection” handler

Parameters:

  • state (String) —

    the state you want to register for

  • block (Block) —

    the block to execute on state changes

Yields:

  • (connection, event) —

    yields your block with



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# File 'lib/z_k/event_handler.rb', line 58

def register_state_handler(state, &block)
  register(state_key(state), &block)
end

#safe_call(callbacks, *args) ⇒ Object (protected) 



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# File 'lib/z_k/event_handler.rb', line 192

def safe_call(callbacks, *args)
  while cb = callbacks.shift
    begin
      cb.call(*args) if cb.respond_to?(:call)
    rescue Exception => e
      logger.error { "Error caught in user supplied callback" }
      logger.error { e.to_std_format }
    end
  end
end

#setup_watcher!(watch_type, opts) ⇒ Object

implements not only setting up the watcher callback, but deduplicating event delivery. Keeps track of in-flight watcher-type+path requests and doesn’t re-register the watcher with the server until a response has been fired. This prevents one event delivery to every callback per :watch => true argument.



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# File 'lib/z_k/event_handler.rb', line 154

def setup_watcher!(watch_type, opts)
  return unless opts.delete(:watch)

  synchronize do
    set = @outstanding_watches.fetch(watch_type)
    path = opts[:path]

    if set.add?(path)
      # this path has no outstanding watchers, let it do its thing
      opts[:watcher] = watcher_callback 
    else
      # outstanding watch for path and data pair already exists, so ignore
#           logger.debug { "outstanding watch request for path #{path.inspect} and watcher type #{watch_type.inspect}, not re-registering" }
    end
  end
end

#state_key(arg) ⇒ Object (protected) 



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# File 'lib/z_k/event_handler.rb', line 176

def state_key(arg)
  int = 
    case arg
    when String, Symbol
      ZookeeperConstants.const_get(:"ZOO_#{arg.to_s.upcase}_STATE")
    when Integer
      arg
    else
      raise NameError # ugh lame
    end

  "state_#{int}"
rescue NameError
  raise ArgumentError, "#{arg} is not a valid zookeeper state", caller
end

#synchronize ⇒ Object

:nodoc:



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# File 'lib/z_k/event_handler.rb', line 137

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

#unregister(*args) ⇒ Object Also known as: unsubscribe

Deprecated.

use #unsubscribe on the subscription object

See Also:

  • ZooKeeper::EventHandlerSubscription#unsubscribe


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# File 'lib/z_k/event_handler.rb', line 74

def unregister(*args)
  if args.first.is_a?(EventHandlerSubscription)
    subscription = args.first
  elsif args.first.is_a?(String) and args[1].is_a?(EventHandlerSubscription)
    subscription = args[1]
  else
    path, index = args[0..1]
    synchronize { @callbacks[path][index] = nil }
    return
  end

  synchronize do
    ary = @callbacks[subscription.path]

    idx = ary.index(subscription) and ary.delete_at(idx)
  end

  nil
end

#unregister_state_handler(*args) ⇒ Object

Deprecated.

use #unsubscribe on the subscription object

See Also:

  • ZooKeeper::EventHandlerSubscription#unsubscribe


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# File 'lib/z_k/event_handler.rb', line 64

def unregister_state_handler(*args)
  if args.first.is_a?(EventHandlerSubscription)
    unregister(args.first)
  else
    unregister(state_key(args.first), args[1])
  end
end

#watcher_callback ⇒ Object (protected) 



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# File 'lib/z_k/event_handler.rb', line 172

def watcher_callback
  ZookeeperCallbacks::WatcherCallback.create { |event| process(event) }
end