README
What Is This?
This package provides several examples that demonstrate various inter-node communcations in ROS 2.
This package consists of the following examples:
add_two_ints_clientlistener_serialized_messagereuse_timeradd_two_ints_client_asynclist_parametersset_and_get_parametersadd_two_ints_serverlist_parameters_asyncset_and_get_parameters_asyncallocator_tutorialone_off_timerset_parameters_callbackcontent_filtering_publisherparameter_blackboardtalkercontent_filtering_subscriberparameter_event_handlertalker_loaned_messageeven_parameters_nodeparameter_eventstalker_serialized_messagelistenerparameter_events_asynclistener_best_effortmatched_event_detect
Build
Run the command below to compile the demo_nodes_cpp ROS 2 package:
colcon build --packages-up-to demo_nodes_cpp
Note: By default, the demo executables will spin up the SingleThreaded executor if run in separate processes, i.e., not composed in the same component container.
To configure the demo executables to run with a different executor, build the package with the custom DEMO_EXECUTOR flag set to the fully qualified name of the executor.
For example, to run with the experimental EventsExecutor,
colcon build --packages-select demo_nodes_cpp --cmake-args -DDEMO_EXECUTOR:STRING=rclcpp::experimental::executors::EventsExecutor
Run
Basic Talker & Listener
This runs a basic ROS 2 publisher and subscriber that exchanges the following string message with an incrementing integer:
Hello World: <count_>
Talker
# Open new terminal
ros2 run demo_nodes_cpp talker
Listener [Default]
# Open new terminal
ros2 run demo_nodes_cpp listener
Listener [Best Effort]
Compared to Listener [Default], listener_best_effort runs a ROS 2 subscriber node that sets the Quality of Service (QoS) Reliability setting to Best Effort via the use of rclcpp::SensorDataQoS, as opposed to the default Reliable.
Messages sent using this policy configuration attempts to deliver samples but may lose them if the network is not robust.
# Open new terminal
ros2 run demo_nodes_cpp listener_best_effort
Basic Server & Client
This runs a ROS 2 server that provides a service to process two integers, outputting the sum back to ROS 2 client node.
Server
# Open new terminal
ros2 run demo_nodes_cpp add_two_ints_server
Client [Synchronous]
# Open new terminal
ros2 run demo_nodes_cpp add_two_ints_client
Client [Asynchronous]
# Open new terminal
ros2 run demo_nodes_cpp add_two_ints_client_async
One-Off Timer
This runs one_off_timer that runs a periodic timer callback that cancels and creates a Wall Timer every 3 callbacks.
ros2 run demo_nodes_cpp one_off_timer
Reuse Timer
Similar to the previous demo, reuse_timer runs a periodic timer callback that reuses the same Wall Timer every 3 callbacks.
ros2 run demo_nodes_cpp reuse_timer
Serialized Messaging
This runs talker_serialized_message ROS 2 node that publishes a manual CDR serialization of the same string message.
# Open new terminal
ros2 run demo_nodes_cpp talker_serialized_message
This runs listener_serialized_message ROS 2 node that subscribes and prints out the serialized string message published by talker_serialized_message.
# Open new terminal
ros2 run demo_nodes_cpp listener_serialized_message
Content-Filter Messaging
This runs content_filtering_subscriber and content_filtering_publisher ROS 2 nodes which exchanges temperature data on the /temperature topic.
However the subscriber requests that data is only sent if the temperature is less than -30 C or greater than 100 C, saving bandwidth.
# Open new terminal
ros2 run demo_nodes_cpp content_filtering_subscriber
# Open new terminal
ros2 run demo_nodes_cpp content_filtering_publisher
List Parameters
This runs list_parameters ROS 2 node which simply programmatically list example parameter names and prefixes:
Synchronous
# Open new terminal
ros2 run demo_nodes_cpp list_parameters
Asynchronous
# Open new terminal
ros2 run demo_nodes_cpp list_parameters_async
Set & Get Parameters
This runs set_and_get_parameters ROS 2 node which programmatically sets and gets parameters.
Synchronous
# Open new terminal
ros2 run demo_nodes_cpp set_and_get_parameters
Asynchronous
# Open new terminal
ros2 run demo_nodes_cpp set_and_get_parameters_async
Allocator Tutorial
This runs allocator_tutorial ROS 2 node that publishes a std_msgs/msg/UInt32 message that contains an integer representing the number of allocations and deallocations that happened during the program.
# Open new terminal
ros2 run demo_nodes_cpp allocator_tutorial
Parameter Events
This runs parameter_events/parameter_events_async ROS 2 node(s) which initiates 10 parameter events which changes an example string parameter.
foo -> bar -> baz -> foobar -> foo -> bar -> baz -> foobar -> foo -> bar
Synchronous
# Open new terminal
ros2 run demo_nodes_cpp parameter_events
Asynchronous
# Open new terminal
ros2 run demo_nodes_cpp parameters_events_async
Even Parameters Node
This runs even_parameters_node ROS 2 node which shows a parameter callback that rejects all parameter updates except those that set an even integer.
# Open new terminal
ros2 run demo_nodes_cpp even_parameters_node
Set Parameters Callback
This runs set_parameters_callback ROS 2 node which triggers a callback when ROS 2 double parameter param1 is set.
The callback then sets ROS 2 double parameter param2 to a fixed 4.0.
# Open new terminal
ros2 run demo_nodes_cpp set_parameters_callback
Parameter Blackboard
This runs parameter_blackboard ROS 2 node which instantiates a ROS 2 parameter server which acts as a global “blackboard” for all nodes to get and set parameters.
# Open new terminal
ros2 run demo_nodes_cpp parameter_blackboard
Parameter Event Handler
This runs parameter_event_handler ROS 2 node which monitors changes to the following parameters:
node: “this_node” parameter: “an_int_param”
node: "/a_namespace/a_remote_node" parameter: "a_string_param"
# Open new terminal
ros2 run demo_nodes_cpp parameter_event_handler
Loaned Messager Talker
This runs loaned_message_talker ROS 2 node that publishes unique messages which eliminates unnecessary copies throughout the ROS 2 stack to maximize performance.
# Open new terminal
ros2 run demo_nodes_cpp talker_loaned_message
Matched Event Detect
This runs 3 ROS 2 nodes.
matched_event_detect_node node that set matched event callback for publisher and subscription separately to output connection or disconnection information.
multi_sub_node create/destroy subscriptions which connect the publisher of matched_event_detect_node.
multi_pub_node create/destroy publishers which connect the subscription of matched_event_detect_node.
# Open new terminal
ros2 run demo_nodes_cpp matched_event_detect
Verify
Basic Talker & Listener
When executed correctly, strings should be printed to terminal similar to what is shown below:
# In terminal running talker
[INFO] [1674551635.122315831] [talker]: Publishing: 'Hello World: 1'
[INFO] [1674551636.122275756] [talker]: Publishing: 'Hello World: 2'
[INFO] [1674551637.122274384] [talker]: Publishing: 'Hello World: 3'
[INFO] [1674551638.122235965] [talker]: Publishing: 'Hello World: 4'
[INFO] [1674551639.122277484] [talker]: Publishing: 'Hello World: 5'
#...
# In terminal running listener/listener_best_effort
[INFO] [1674551636.122881229] [listener]: I heard: [Hello World: 1]
[INFO] [1674551637.122832606] [listener]: I heard: [Hello World: 2]
[INFO] [1674551638.122675099] [listener]: I heard: [Hello World: 3]
[INFO] [1674551639.122788087] [listener]: I heard: [Hello World: 4]
[INFO] [1674551640.122850575] [listener]: I heard: [Hello World: 5]
#...
Basic Server & Client
When executed correctly, strings should be printed to terminal similar to what is shown below:
Server
# In terminal running add_two_ints_server
[INFO] [1674553268.912391774] [add_two_ints_server]: Incoming request
a: 2 b: 3
Client [Synchronous]
# In terminal running add_two_ints_client
[INFO] [1674553268.912602310] [add_two_ints_client]: Result of add_two_ints: 5
Client [Asynchronous]
# In terminal running add_two_ints_client_async
[INFO] [1674553718.598690033] [add_two_ints_client]: Result of add_two_ints: 5
One-Off Timer
When executed correctly, strings should be printed to terminal similar to what is shown below:
# In terminal running one_off_timer
[INFO] [1674552840.400680444] [one_off_timer]: in periodic_timer callback
[INFO] [1674552840.400915092] [one_off_timer]: resetting one off timer
[INFO] [1674552841.401204072] [one_off_timer]: in one_off_timer callback
[INFO] [1674552842.400698264] [one_off_timer]: in periodic_timer callback
[INFO] [1674552842.400819311] [one_off_timer]: not resetting one off timer
[INFO] [1674552844.400695640] [one_off_timer]: in periodic_timer callback
[INFO] [1674552844.400819933] [one_off_timer]: not resetting one off timer
[INFO] [1674552846.400684373] [one_off_timer]: in periodic_timer callback
[INFO] [1674552846.400799868] [one_off_timer]: resetting one off timer
[INFO] [1674552847.400948238] [one_off_timer]: in one_off_timer callback
[INFO] [1674552848.400703699] [one_off_timer]: in periodic_timer callback
[INFO] [1674552848.400828811] [one_off_timer]: not resetting one off timer
[INFO] [1674552850.400680424] [one_off_timer]: in periodic_timer callback
[INFO] [1674552850.400775977] [one_off_timer]: not resetting one off timer
[INFO] [1674552852.400690511] [one_off_timer]: in periodic_timer callback
[INFO] [1674552852.400815404] [one_off_timer]: resetting one off timer
[INFO] [1674552853.401060139] [one_off_timer]: in one_off_timer callback
#...
Notice how the timer is reset only after two callback iterations.
Reuse Timer
When executed correctly, strings should be printed to terminal similar to what is shown below:
[INFO] [1674554333.056000613] [reuse_timer]: in periodic_timer callback
[INFO] [1674554333.056432269] [reuse_timer]: resetting one off timer
[INFO] [1674554334.056732370] [reuse_timer]: in one_off_timer callback
[INFO] [1674554335.055978249] [reuse_timer]: in periodic_timer callback
[INFO] [1674554335.056111777] [reuse_timer]: not resetting one off timer
[INFO] [1674554337.055978910] [reuse_timer]: in periodic_timer callback
[INFO] [1674554337.056108925] [reuse_timer]: not resetting one off timer
[INFO] [1674554339.055966108] [reuse_timer]: in periodic_timer callback
[INFO] [1674554339.056083983] [reuse_timer]: resetting one off timer
[INFO] [1674554340.056295399] [reuse_timer]: in one_off_timer callback
#...
Same as One-Off Timer.
Serialized Messaging
When executed correctly, strings should be printed to terminal similar to what is shown below:
# In terminal running talker_serialized_message
ROS message:
Hello World:1
serialized message:
00 01 00 00 0e 00 00 00 48 65 6c 6c 6f 20 57 6f 72 6c 64 3a 31 00
ROS message:
Hello World:2
serialized message:
00 01 00 00 0e 00 00 00 48 65 6c 6c 6f 20 57 6f 72 6c 64 3a 32 00
ROS message:
Hello World:3
serialized message:
00 01 00 00 0e 00 00 00 48 65 6c 6c 6f 20 57 6f 72 6c 64 3a 33 00
# In terminal running listerner_serialized_message
I heard data of length: 24
00 01 00 00 0e 00 00 00 48 65 6c 6c 6f 20 57 6f 72 6c 64 3a 32 00 00 00
serialized data after deserialization: Hello World:2
I heard data of length: 24
00 01 00 00 0e 00 00 00 48 65 6c 6c 6f 20 57 6f 72 6c 64 3a 33 00 00 00
serialized data after deserialization: Hello World:3
I heard data of length: 24
00 01 00 00 0e 00 00 00 48 65 6c 6c 6f 20 57 6f 72 6c 64 3a 34 00 00 00
serialized data after deserialization: Hello World:4
#...
Content-Filtering Messaging
When executed correctly, strings should be printed to terminal similar to what is shown below:
# In terminal running content_filtering_publisher
[INFO] [1674563203.567530898] [content_filtering_publisher]: Publishing: '-100.000000'
[INFO] [1674563204.567508197] [content_filtering_publisher]: Publishing: '-90.000000'
[INFO] [1674563205.567517142] [content_filtering_publisher]: Publishing: '-80.000000'
#...
# In terminal running content_filtering_subscriber
[INFO] [1674563182.873825084] [content_filtering_subscriber]: subscribed to topic "/temperature" with content filter options "data < %0 OR data > %1, {-30.000000, 100.000000}"
[INFO] [1674563203.568310361] [content_filtering_subscriber]: I receive an emergency temperature data: [-100.000000]
[INFO] [1674563204.568128370] [content_filtering_subscriber]: I receive an emergency temperature data: [-90.000000]
[INFO] [1674563205.568082783] [content_filtering_subscriber]: I receive an emergency temperature data: [-80.000000]
#...
List Parameters [Synchronous/Asynchronous]
When executed correctly, strings should be printed to terminal similar to what is shown below:
[INFO] [1674563905.346022942] [list_parameters]: Setting parameters...
[INFO] [1674563905.347158439] [list_parameters]: Listing parameters...
[INFO] [1674563905.347570888] [list_parameters]:
Parameter names:
bar
foo
foo.first
foo.second
Parameter prefixes:
foo
Set & Get Parameters [Synchronous/Asynchronous]
When executed correctly, strings should be printed to terminal similar to what is shown below:
[INFO] [1674564137.057616328] [set_and_get_parameters]:
Parameter name: foo
Parameter value (integer): 2
Parameter name: baz
Parameter value (double): 1.450000
Parameter name: foobarbaz
Parameter value (bool_array): [true, false]
Parameter name: toto
Parameter value (byte_array): [0xff, 0x7f]
Allocator Tutorial
When executed correctly, strings should be printed to terminal similar to what is shown below:
This simple demo shows off a custom memory allocator to count all
instances of new/delete in the program. It can be run in either regular
mode (no arguments), or in intra-process mode (by passing 'intra' as a
command-line argument). It will then publish a message to the
'/allocator_tutorial' topic every 10 milliseconds until Ctrl-C is pressed.
At that time it will print a count of the number of allocations and
deallocations that happened during the program.
Intra-process pipeline is OFF.
Run ros2 topic echo /allocator_tutorial to see the output in the ROS 2 topic, /allocator_tutorial:
# Open new terminal
data: 224
---
data: 228
---
data: 230
---
data: 231
---
data: 233
---
data: 234
---
data: 235
---
Parameter Events [Synchronous/Asynchronous]
When executed correctly, strings should be printed to terminal similar to what is shown below:
[INFO] [1674565202.370104660] [parameter_events]:
Parameter event:
new parameters:
foo
changed parameters:
deleted parameters:
[INFO] [1674565202.370241604] [parameter_events]:
Parameter event:
new parameters:
bar
changed parameters:
deleted parameters:
[INFO] [1674565202.370303487] [parameter_events]:
Parameter event:
new parameters:
baz
changed parameters:
deleted parameters:
[INFO] [1674565202.370355113] [parameter_events]:
Parameter event:
new parameters:
foobar
changed parameters:
deleted parameters:
[INFO] [1674565202.370398069] [parameter_events]:
Parameter event:
new parameters:
changed parameters:
foo
deleted parameters:
[INFO] [1674565202.370424143] [parameter_events]:
Parameter event:
new parameters:
changed parameters:
bar
deleted parameters:
[INFO] [1674565202.370447765] [parameter_events]:
Parameter event:
new parameters:
changed parameters:
baz
deleted parameters:
[INFO] [1674565202.370470405] [parameter_events]:
Parameter event:
new parameters:
changed parameters:
foobar
deleted parameters:
[INFO] [1674565202.370492871] [parameter_events]:
Parameter event:
new parameters:
changed parameters:
foo
deleted parameters:
[INFO] [1674565202.370515168] [parameter_events]:
Parameter event:
new parameters:
changed parameters:
bar
deleted parameters:
Even Parameters Node
Run ros2 param set /even_parameters_node myint 2 to set the parameter to a valid even integer and produce a similar result like below:
[INFO] [1674566014.892688389] [even_parameters_node]: parameter 'myint' has changed and is now: 2
Run ros2 param set /even_parameters_node myint 3 to set the parameter to an invalid odd integer and produce a similar result like below:
[INFO] [1674566088.870030436] [even_parameters_node]: Requested value '3' for parameter 'myint' is not an even number: rejecting change...
Set Parameters Callback
[Before]
Run ros2 param get /set_param_callback_node param1 should print the following to terminal:
Double value is: 0.0
Run ros2 param get /set_param_callback_node param2 should print the following to terminal:
Double value is 0.0
[Change]
Run ros2 param set set_param_callback_node param1 10.0 and see it fail with
Setting parameter failed: cannot set 'param1' > 5.0
Run ros2 param set set_param_callback_node param1 3.0
Set parameter successful
[After]
Run ros2 param get /set_param_callback_node param1 should print the following to terminal:
Double value is: 28.0
Run ros2 param get /set_param_callback_node param2 should print the following to terminal:
Double value is 4.0
Parameter Blackboard
When executed correctly, strings should be printed to terminal similar to what is shown below:
INFO] [1674568261.762813104] [parameter_blackboard]: Parameter blackboard node named '/parameter_blackboard' ready, and serving '5' parameters already!
Running ros2 param list should reveal the 6 parameters served:
/parameter_blackboard:
qos_overrides./parameter_events.publisher.depth
qos_overrides./parameter_events.publisher.durability
qos_overrides./parameter_events.publisher.history
qos_overrides./parameter_events.publisher.reliability
start_type_description_service
use_sim_time
Parameter Event Handler
Run ros2 param set this_node an_int_param 21 in a new terminal will produce the following results:
# In terminal running parameter_event_handler
[INFO] [1674569608.306038487] [this_node]: cb1: Received an update to parameter "an_int_param" of type integer: "21"
[INFO] [1674569608.306356753] [this_node]: cb3: Received an update to parameter "an_int_param" of type: integer: "21"
Run ros2 param set /a_namespace/a_remote_node a_string_param "string value to set" in a new terminal will produce the following results:
[INFO] [1674569622.728945232] [this_node]: cb2: Received an update to parameter "a_string_param" of type: string: "string value to set"
[INFO] [1674569622.729143396] [this_node]: cb3: Received an update to parameter "a_string_param" of type: string: "string value to set"
[INFO] [1674569622.729246614] [this_node]: cb3: Received an update to parameter "a_string_param" of type: string: "string value to set"
Loaned Message Talker
When executed correctly, strings should be printed to terminal similar to what is shown below:
# In terminal running loaned_message_talker
[INFO] [1674570146.112222368] [loaned_message_talker]: Publishing: 'Hello World: 1'
[INFO] [1674570147.111670599] [loaned_message_talker]: Publishing: '2.000000'
[INFO] [1674570147.111853637] [loaned_message_talker]: Publishing: 'Hello World: 2'
[INFO] [1674570148.111662758] [loaned_message_talker]: Publishing: '3.000000'
[INFO] [1674570148.111804226] [loaned_message_talker]: Publishing: 'Hello World: 3'
[INFO] [1674570149.111651863] [loaned_message_talker]: Publishing: '4.000000'
[INFO] [1674570149.111819520] [loaned_message_talker]: Publishing: 'Hello World: 4'
Note that Fast-DDS does not support the loaned messages. The loaned message API is used in iceoryx right now, which workes with CycloneDDS.
Matched Event Detect
When executed correctly, strings should be printed to terminal similar to what is shown below:
# In terminal running matched_event_detect
[INFO] [1679887690.127684740] [multi_sub_node]: Create a new subscription.
[INFO] [1679887690.128090105] [matched_event_detect_node]: First subscription is connected.
[INFO] [1679887690.128836774] [multi_sub_node]: Create a new subscription.
[INFO] [1679887690.129157780] [matched_event_detect_node]: The changed number of connected subscription is 1 and current number of connected subscription is 2.
[INFO] [1679887690.129193220] [multi_sub_node]: Destroy a subscription.
[INFO] [1679887690.130552475] [matched_event_detect_node]: The changed number of connected subscription is -1 and current number of connected subscription is 1.
[INFO] [1679887690.130588555] [multi_sub_node]: Destroy a subscription.
[INFO] [1679887690.131355128] [matched_event_detect_node]: Last subscription is disconnected.
[INFO] [1679887690.132014952] [multi_pub_node]: Create a new publisher.
[INFO] [1679887690.132262901] [matched_event_detect_node]: First publisher is connected.
[INFO] [1679887690.132898522] [multi_pub_node]: Create a new publisher.
[INFO] [1679887690.133143624] [matched_event_detect_node]: The changed number of connected publisher is 1 and current number of connected publisher is 2.
[INFO] [1679887690.133178687] [multi_pub_node]: Destroy a publisher.
[INFO] [1679887690.134139929] [matched_event_detect_node]: The changed number of connected publisher is -1 and current number of connected publisher is 1.
[INFO] [1679887690.134176647] [multi_pub_node]: Destroy a publisher.
[INFO] [1679887690.134887946] [matched_event_detect_node]: Last publisher is disconnected.
FAQ
Q: Encountered the following error in terminal when running Loaned Message Talker:
[INFO] [1674570146.112148792] [rclcpp]: Currently used middleware can't loan messages. Local allocator will be used.
A: Ensure that CycloneDDS RMW is used by running export RMW_IMPLEMENTATION=rmw_cyclonedds_cpp.