extract.rb

### in lib/ruote/engine.rb

    # Quick note : the implementation of launch is found in the module
    # Ruote::ReceiverMixin that the engine includes.
    #
    # Some processes have to have one and only one instance of themselves
    # running, these are called 'singles' ('singleton' is too object-oriented).
    #
    # When called, this method will check if an instance of the pdef is
    # already running (it uses the process definition name attribute), if
    # yes, it will return without having launched anything. If there is no
    # such process running, it will launch it (and register it).
    #
    # TODO : explain return value
    #
    def launch_single (process_definition, fields={}, variables={})

      tree = @context.parser.parse(process_definition)
      name = tree[1]['name'] || (tree[1].find { |k, v| v.nil? } || []).first

      raise ArgumentError.new(
        'process definition is missing a name, cannot launch as single'
      ) unless name

      singles = @context.storage.get('variables', 'singles') || {
        '_id' => 'singles', 'type' => 'variables', 'h' => {}
      }
      wfid = singles['h'][name]

      # TODO : what if reserved ?

      return wfid if wfid && process(wfid) != nil

      singles['h'][name] = '(reserved)'
      r = @context.storage.put('variables', singles)

      return launch_single(tree, fields, variables) unless r.nil?
        #
        # reservation of the name failed, get back to the "start"...
        #
        # all this to prevent races between multiple engines...

      wfid = launch(tree, fields, variables)

      singles['h'][name] = wfid
      r = @context.storage.put('variables', singles)

      # TODO : what if r != nil ? Can this happen ?

      wfid
    end


### test/functional/ft_46_launch_single.rb

class FtLaunchSingleTest < Test::Unit::TestCase
  include FunctionalBase

  def test_no_name_singles_are_rejected

    assert_raise ArgumentError do
      @engine.launch_single(Ruote.process_definition do
        wait '2y'
        echo 'over.'
      end)
    end
  end

  def test_launch_single

    pdef = Ruote.process_definition 'unique_process' do
      wait '2y'
      echo 'over.'
    end

    wfid = @engine.launch_single(pdef)

    p @engine.storage.get('variables', 'singles')

    # TODO : continue here
  end
end