Ruote::EngineParticipant

A participant for pushing the execution of [segments of] processes to other engines.

It works by giving the participant the connection information to the storage of the other engine.

For instance :

engine0 =
  Ruote::Engine.new(
    Ruote::Worker.new(
      Ruote::FsStorage.new('work0', 'engine_id' => 'engine0')))
engine1 =
  Ruote::Engine.new(
    Ruote::Worker.new(
      Ruote::FsStorage.new('work1', 'engine_id' => 'engine1')))

engine0.register_participant('engine1',
  Ruote::EngineParticipant,
  'storage_class' => Ruote::FsStorage,
  'storage_path' => 'ruote/storage/fs_storage',
  'storage_args' => 'work1')
engine1.register_participant('engine0',
  Ruote::EngineParticipant,
  'storage_class' => Ruote::FsStorage,
  'storage_path' => 'ruote/storage/fs_storage',
  'storage_args' => 'work0')

In this example, two engines are created (note that their 'engine_id' is explicitely set (else it would default to 'engine')). Each engine is then registered as participant in the other engine. The registration parameters detail the class and the arguments to the storage of the target engine.

This example is a bit dry / flat. A real world example would perhaps detail a 'master' engine connected to 'departmental' engines, something more hierarchical.

The example also binds reciprocally engines. If the delegated processes are always 'forgotten', one could imagine not binding the source engine as a participant in the target engine (not need to answer back).

There are then two variants for calling a subprocess

subprocess :ref => 'subprocess_name', :engine => 'engine1'
  # or
participant :ref => 'engine1', :pdef => 'subprocess_name'

It's OK to go for the shorter versions :

subprocess_name :engine => 'engine1'
  # or
participant 'engine1', :pdef => 'subprocess_name'
engine1 :pdef => 'subprocess_name'

The subprocess is defined in the current process, or it's given via its URL. The third variant is a subprocess bound as an engine variable.

engine.variables['variant_3'] = Ruote.process_definition do
  participant 'hello_world_3'
end

pdef = Ruote.process_definition do
  sequence do
    engine1 :pdef => 'variant_1'
    engine1 :pdef => 'http://pdefs.example.com/variant_2.rb'
    engine1 :pdef => 'variant_3'
  end
  define 'variant_1' do
    participant 'hello_world_1'
  end
end