Introduction

ROS2 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 are scoped within a state machine of a finite amount of 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 ROS2 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 different 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 followed.

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

The principle is implemented in this demo as the typical talker/listener demo. However, imaging a real scenario with attached hardware which may have a rather long booting phase, i.e. a laser or camera. One could image bringing up the device driver in the configuring state, start and stop only the publishing of the device's data and only in the cleanup/shutdown phase actually shutdown the device.

The lifecycle_listener is a simple listener which shows the characteristics of the lifecycle talker. The talker enables the message publishing only in the active state and thus making the listener receiving only 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 ROS2 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 (as of ROS 2 Bouncy):

ros2 launch lifecycle lifecycle_demo.launch.py

File truncated at 100 lines see the full file

Changelog for package lifecycle

0.8.4 (2019-11-19)

0.8.3 (2019-11-11)

0.8.2 (2019-11-08)

• Remove unnecessary dependency on ros2run (#413)
• Contributors: Michel Hidalgo

0.8.1 (2019-10-23)

• Replace ready_fn with ReadyToTest action (#404)
• Contributors: Peter Baughman

0.8.0 (2019-09-26)

• Fix lifecycle_service_client namespace (#369)
• Contributors: Cameron Evans

0.7.6 (2019-05-30)

0.7.5 (2019-05-29)

• Update asciinema recordings (#360)
• Use rate instead of thread::sleep to react to Ctrl-C (#348)
• Contributors: Dirk Thomas, Karsten Knese

0.7.4 (2019-05-20)

• Add lifecycle rostest (#336)
• Contributors: Michel Hidalgo

0.7.3 (2019-05-10)

0.7.2 (2019-05-08)

• changes to avoid deprecated API's (#332)
• Corrected publish calls with shared_ptr signature (#327)
• Contributors: William Woodall, ivanpauno

0.7.1 (2019-04-26)

0.7.0 (2019-04-14)

• Updated for NodeOptions Node constructor. (#308)
• Contributors: Michael Carroll

0.6.2 (2019-01-15)

• Added readme.rst (#300)
• Contributors: Karsten Knese

0.6.1 (2018-12-13)

0.6.0 (2018-12-07)

• Cleaned up lifecycle demo (#283)
• Updated for refactoring in rclcpp (#276)
• Added semicolons to all RCLCPP and RCUTILS macros. (#278)
• Fixed typo in comment (#270)
• Contributors: Chris Lalancette, Karsten Knese, Yutaka Kondo

0.5.1 (2018-06-28)

0.5.0 (2018-06-27)

• Converted launch files to the new launch style. (#262)
• Updated to support remapping arguments to python nodes by passing unused arguments to rclpy from argparse. (#252)
• Updated to handle change in signature to get_service_name. (#245)
• Updated launch files to account for the "old launch" getting renamespaced as launch -> launch.legacy. (#239)
• Updated service client demos to handle multiple requests. (#228)
• Contributors: Geoffrey Biggs, Kevin Allen, Shane Loretz, William Woodall, dhood