Introduction

ROS 2 introduces the concept of managed nodes, also called LifecycleNodes. In the following tutorial, we explain the purpose of these nodes, what makes them different from regular nodes and how they comply to a lifecycle management. Managed nodes contain a state machine with a set of predefined states. These states can be changed by invoking a transition id which indicates the succeeding consecutive state. The state machine is implemented as described at the ROS 2 design page.

Our implementation differentiates between Primary States and Transition States. Primary States are supposed to be steady states in which any node can do the respected task. On the other hand, Transition States are meant as temporary intermediate states attached to a transition. The result of these intermediate states are used to indicate whether a transition between two primary states is considered successful or not. Thus, any managed node can be in one of the following states:

Primary States (steady states):

• unconfigured
• inactive
• active
• shutdown

Transition States (intermediate states):

• configuring
• activating
• deactivating
• cleaningup
• shuttingdown

The possible transitions to invoke are:

• configure
• activate
• deactivate
• cleanup
• shutdown

For a more verbose explanation on the applied state machine, we refer to the design page which provides an in-detail explanation about each state and transition.

The demo

What's happening

The demo is split into 3 separate applications:

• lifecycle_talker
• lifecycle_listener
• lifecycle_service_client

The lifecycle_talker represents a managed node and publishes according to which state the node is in. We split the tasks of the talker node into separate pieces and execute them as follows:

1. configuring: We initialize our publisher and timer
2. activate: We activate the publisher and timer in order to enable a publishing
3. deactivate: We stop the publisher and timer
4. cleanup: We destroy the publisher and timer

This demo shows a typical talker/listener pair of nodes. However, imagine a real scenario with attached hardware which may have a rather long booting phase, i.e. a laser or camera. One could imagine bringing up the device driver in the configuring state, start and stop only the publishing of the device's data in active/deactive state, and only in the cleanup/shutdown state actually shutdown the device.

The lifecycle_listener is a simple listener which shows the characteristics of the lifecycle talker. The talker enables message publishing only in the active state and thus the listener only receives messages when the talker is in an active state.

The lifecycle_service_client is a script calling different transitions on the lifecycle_talker. This is meant as the external user controlling the lifecycle of nodes.

Run the demo

In order to run this demo, we open three terminals and source our ROS 2 environment variables either from the binary distributions or the workspace we compiled from source.

lifecycle_talker lifecycle_listener lifecycle_service_client ———————————————————————————— ———————————————————————————— ———————————————————————————— $ ros2 run lifecycle lifecycle_talker $ ros2 run lifecycle lifecycle_listener $ ros2 run lifecycle lifecycle_service_client

Alternatively, these three programs can be run together in the same terminal using the launch file:

ros2 launch lifecycle lifecycle_demo.launch.py

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Changelog for package lifecycle

0.20.5 (2024-07-26)

0.20.4 (2024-05-15)

0.20.3 (2023-01-10)

0.20.2 (2022-05-10)

0.20.1 (2022-04-08)

• Make lifecycle demo automatically exit when done (#558)
• Contributors: Shane Loretz

0.20.0 (2022-03-01)

• Use default on_activate()/on_deactivate() implemenetation of Node (#552)
• Contributors: Ivan Santiago Paunovic

0.19.0 (2022-01-14)

0.18.0 (2021-12-17)

• Update maintainers to Audrow Nash and Michael Jeronimo (#543)
• Contributors: Audrow Nash

0.17.0 (2021-10-18)

• Fix use of future in lifecycle demo (#534)
• Fixing deprecated subscriber callback warnings (#532)
• Contributors: Abrar Rahman Protyasha, Christophe Bedard

0.16.0 (2021-08-11)

0.15.0 (2021-05-14)

0.14.2 (2021-04-26)

• Cleanup the README.rst for the lifecycle demo. (#508)
• Contributors: Chris Lalancette

0.14.1 (2021-04-19)

0.14.0 (2021-04-06)

• change ParameterEventHandler to take events as const ref instead of shared pointer (#494)
• Contributors: William Woodall

0.13.0 (2021-03-25)

0.12.1 (2021-03-18)

0.12.0 (2021-01-25)

0.11.0 (2020-12-10)

• Update the package.xml files with the latest Open Robotics maintainers (#466)
• Contributors: Michael Jeronimo

0.10.1 (2020-09-21)

• Add missing required parameter in LifecycleNode launch action (#456)
• Contributors: Ivan Santiago Paunovic

0.10.0 (2020-06-17)

0.9.3 (2020-06-01)

0.9.2 (2020-05-26)

• Fix typo (#445)
• Replace ros2 msg command in lifecycle README (#446)
• Contributors: Audrow Nash, Shota Aoki

0.9.1 (2020-05-12)

0.9.0 (2020-04-30)

• Replace deprecated launch_ros usage (#437)
• Update launch_ros action usage (#431)
• code style only: wrap after open parenthesis if not in one line (#429)
• Contributors: Dirk Thomas, Jacob Perron

0.8.4 (2019-11-19)

0.8.3 (2019-11-11)

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