Conceptually, the execution of Orocos tasks is split into two parts. First, the task encapsulates the so-called “computation” part of the component. It is declared and developed, but how it should be executed is left out. Second, it is deployed: The task is associated with a trigger mechanism that defines when the task’s computation should be executed.

Until now, you have used deployments implicitly as, for each task, oroGen defines a default deployment for convenience reasons. The default deployment execution schema is given in the task description by statements like periodic(1.0) or port_driven. Furthermore, the default deployments add a logging component by default and each task is run as a separate process.

In order to allow a more flexible definition of the execution schema and putting multiple tasks into one process, explicit deployments can also be specified. They override the default deployment of the task. For further information, also have a look at the documentation page.

Deployments are specified in an orogen project, the same way as tasks are. Even though it is possible to define deployments in the same orogen file as the tasks, that is not recommended. Best practice is to create a separate oroGen project for all your deployments, in order to keep an overview of how all the tasks on your system are defined.

Defining deployments

Let’s get back to the initial messenger example. The periodicity was set to 1.0 seconds for the default deployment. Let’s assume now that the task should be executed at a higher rate. Create a new oroGen project (for instance in tutorials/orogen):

rock-create-orogen messenger_deployments

When asked for dependencies, give the message producer and consumer task projects, e.g.:

tutorials/orogen/message_producer, tutorials/orogen/message_consumer

In the file messenger_deployments.orogen delete the content and add the following:

name "messenger_deployments"

using_task_library "message_producer"

deployment "faster_message_producer" do 
    task("producer","message_producer::Task").periodic(0.1)
end

Finalize the package creation with (in the same directory than the oroGen file)

rock-create-orogen

And, finally, the usual

amake

Usage in Ruby scripts

The defined deployments are used in Ruby scripts by replacing the model_name => task_name syntax with the deployment name. Moreover, the Orocos.name_service.get stanzas must use the task names declared in the specific deployments (first argument to the “task” statement, as e.g. producer above). Using the explicit deployment above for the messenger example script, while keeping the default deployment for the consumer would be done with:

require 'orocos'
require 'readline'

include Orocos
Orocos.initialize

Orocos.run 'faster_message_producer',
    'messages::Consumer' => 'consumer' do  
  
  # When using explicit deployments, the name that should be used in
  # Orocos.name_service.get must be the same name than given as first argument of the
  # "task" statement in the deployment definition
  producer = Orocos.name_service.get 'producer'
  consumer = Orocos.name_service.get 'consumer'
  
  # Never assume that a component supports being reconnected
  # at runtime, it might not be the case
  #
  # If you have the choice, connect before the component is
  # even configured
  producer.messages.connect_to consumer.messages
  
  producer.configure
  producer.start
  
  consumer.configure
  consumer.start
  
  Readline::readline("Press ENTER to exit\n")
 
end