Ruote::Exp::SubprocessExpression

An expression for invoking a subprocess.

pdef = Ruote.process_definition do
  sequence do
    subprocess :ref => 'delivering'
    subprocess 'invoicing'
    refill_stock :if => '${v:stock_size} < 10'
  end
  define 'delivering' do
    # ...
  end
  define 'invoicing' do
    # ...
  end
  define 'refill_stock' do
    # ...
  end
end

passing attributes as variables

The attributes of the subprocess expression are passed as variables of the new subprocess instance.

Ruote.process_definition do
  subprocess 'sub0', :a => 'A', :b => 'B'
  define :sub0 do
    echo '${v:a}:${v:b}'
  end
end

This example (and useless) process example will output "A:B" to STDOUT.

passing 'blocks' to subprocesses

When the subprocess expression has children, the first of them is passed to the subprocess instance as the 'tree' variable, readily available for an 'apply' expression.

Ruote.process_definition :name => 'double review' do
  sequence do
    sub0 do
      review_board
    end
    sub0 do
      review_board
    end
  end
  define 'sub0' do
    concurrence do
      apply :i => 0
      apply :i => 1
      apply :i => 2
    end
  end
end

This example will send 2 x 3 concurrent workitems to the participant named 'review_board' (note that it could also be the name of another subprocess).

passing 'parameters' to subprocess

Ruote.process_definition :name => 'whatever' do

  call :who => 'the cops', :when => 'if I\'m not back at 3'

  process_definition 'call' do
    participant :ref => '${v:who}', :msg => 'this is a call'
  end
end

This binds the variables 'who' and 'when' in the subprocess instance.

Of course you can combine parameters and blocks passing.

pointing to subprocesses via their URI

It's OK to invoke subprocesses via a URI

subprocess :ref => 'pdefs/definition1.rb'

or

subprocess :ref => 'http://pdefs.example.org/account/def1.xml'

Remember that the 'remote_definition_allowed' option of the engine has to be set to true for the latter to work, else the engine will refuse to load definitions over HTTP.

Shorter :

subprocess 'http://pdefs.example.org/account/def1.xml'

subprocess URIs bound at engine level

There is a class of variables accessible to process instances in read-only mode : engine level variables.

They can be set via the engine's initialization code (or later) like in this example :

engine.variables['inventory_check'] = 'http://pdefs.example.com/ic0.rb'

All the process instance in the engine may then trigger this process in these 3 ways :

subprocess :ref => 'inventory_check'
subprocess 'inventory_check'
inventory_check

The latter may make process definitions quite readable (but blur the distinction between expressions, call to participants or to subprocesses).