Webgen::Blackboard

A blackboard object provides two features for inter-object communication:

services: An object can add a service to the blackboard which can be called by any other object by just specifing the service name. Therefore it is easy to change the underlying implementation of the service and there are no hard dependencies on specific class or method names.
listeners: Objects may register themselves for specific messsage names and get notified when such a message gets dispatched.

For a list of all available services and messages have a look at the main Webgen documentation page.

Public Class Methods

new() click to toggle source

Create a new Blackboard object.

    # File lib/webgen/blackboard.rb, line 20
20:     def initialize
21:       @listener = {}
22:       @services = {}
23:     end

Public Instance Methods

add_listener(msg_names = nil, callable_object = nil, &block) click to toggle source

Add the callable_object or the given block as listener for the messages msg_names (one message name or an array of message names).

    # File lib/webgen/blackboard.rb, line 27
27:     def add_listener(msg_names = nil, callable_object = nil, &block)
28:       callable_object = callable_object || block
29:       if !callable_object.nil?
30:         raise ArgumentError, "The listener needs to respond to 'call'" unless callable_object.respond_to?(:call)
31:         [msg_names].flatten.compact.each {|name| (@listener[name] ||= []) << callable_object}
32:       else
33:         raise ArgumentError, "You have to provide a callback object or a block"
34:       end
35:     end

add_service(service_name, callable_object = nil, &block) click to toggle source

Add a service named service_name provided by the callable_object or a block to the blackboard.

    # File lib/webgen/blackboard.rb, line 52
52:     def add_service(service_name, callable_object = nil, &block)
53:       callable_object = callable_object || block
54:       if @services.has_key?(service_name)
55:         raise "The service name '#{service_name}' is already taken"
56:       else
57:         raise ArgumentError, "An object providing a service needs to respond to 'call'" unless callable_object.respond_to?(:call)
58:         @services[service_name] = callable_object
59:       end
60:     end

del_listener(msg_names, callable_object) click to toggle source

Remove the given object from the dispatcher queues of the message names specified in msg_names.

    # File lib/webgen/blackboard.rb, line 39
39:     def del_listener(msg_names, callable_object)
40:       [msg_names].flatten.each {|name| @listener[name].delete(callable_object) if @listener[name]}
41:     end

del_service(service_name) click to toggle source

Delete the service service_name.

    # File lib/webgen/blackboard.rb, line 63
63:     def del_service(service_name)
64:       @services.delete(service_name)
65:     end

dispatch_msg(msg_name, *args) click to toggle source

Dispatch the message msg_name to all listeners for this message, passing the given arguments.

    # File lib/webgen/blackboard.rb, line 45
45:     def dispatch_msg(msg_name, *args)
46:       return unless @listener[msg_name]
47:       @listener[msg_name].each {|obj| obj.call(*args)}
48:     end

invoke(service_name, *args, &block) click to toggle source

Invoke the service called service_name with the given arguments.

    # File lib/webgen/blackboard.rb, line 68
68:     def invoke(service_name, *args, &block)
69:       if @services.has_key?(service_name)
70:         @services[service_name].call(*args, &block)
71:       else
72:         raise ArgumentError, "No such service named '#{service_name}' available"
73:       end
74:     end

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