Subscriber

mrs_lib::Subscriber

template<typename MessageType>
class Subscriber

Wrapper for rclcpp::Subscription with callback and polling interface.

Template Parameters:

MessageType – Type of the message to subscribe to.

Public Types

using MessageCallback = std::function<void(std::shared_ptr<const MessageType>)>

Type of the accepted callback.

using MessageCoroCallback = CoroCallback<void(std::shared_ptr<const MessageType>)>

Type of the accepted coroutine callback.

Public Functions

inline explicit Subscriber(const SubscriberOptions &options, std::string_view topic_name, MessageCallback callback)

Construct a Subscriber with the specified callback.

Parameters:

  • options – Options to configure the subscriber.

  • topic_name – Name of the topic to subscribe to.

  • callback – Callback to call when a message is received.

inline explicit Subscriber(const SubscriberOptions &options, std::string_view topic_name, MessageCoroCallback callback)

Construct a Subscriber with the specified coroutine callback.

Parameters:

  • options – Options to configure the subscriber.

  • topic_name – Name of the topic to subscribe to.

  • callback – Coroutine callback to call when a message is received.

inline explicit Subscriber(const SubscriberOptions &options, std::string_view topic_name, PolledSubscriberTag tag)

Construct a Subscriber without any callback.

Parameters:

  • options – Options to configure the subscriber.

  • topic_name – Name of the topic to subscribe to.

  • tag – Tag to explicitly specify that this subscriber has no callback.

std::optional<std::shared_ptr<const MessageType>> get_message()

Get the latest received message, if there is one.

Calling this function marks the message as used.

Returns:

The latest message, if there is any, nullopt otherwise.

std::optional<std::shared_ptr<const MessageType>> get_new_message()

Get the latest new message, if there is one.

A new message is a message that was not yet used. A message is always marked as used if there is a callback associated with the subscriber. Additionally, it is marked as used by obtaining it using get_*message.

Calling this function marks the message as used.

Returns:

The latest new message, if there is any, nullopt otherwise.

std::optional<std::shared_ptr<const MessageType>> peek_message() const

Get the latest received message, if there is one.

Calling this function does NOT mark the message as used.

Returns:

The latest message, if there is any, nullopt otherwise.

std::optional<std::shared_ptr<const MessageType>> peek_new_message() const

Get the latest new message, if there is one.

A new message is a message that was not yet used. A message is always marked as used if there is a callback associated with the subscriber. Additionally, it is marked as used by obtaining it using get_*message.

Calling this function does NOT mark the message as used.

Returns:

The latest new message, if there is any, nullopt otherwise.

rclcpp::Time get_last_message_time() const

Returns time of the last received message on the topic, handled by this Subscriber.

Returns:

time when the last message was received.

std::string get_topic_name() const

Returns the resolved (full) name of the topic handled by this Subscriber.

Returns:

The name of the handled topic.

std::string get_unresolved_topic_name() const

Returns the unresolved name of the topic handled by this Subscriber.

Returns:

The name of the handled topic.

uint32_t get_publisher_count() const

Returns number of publishers registered at the topic.

Returns:

number of publishers.

mrs_lib::SubscriberOptions

struct SubscriberOptions

Options for configuring the Subscriber.

Public Members

SubscriberNodeInterfaces node_interfaces

ROS node interfaces used by the subscriber.

rclcpp::QoS qos = rclcpp::SystemDefaultsQoS()

QOS settings for the subscriber.

std::shared_ptr<rclcpp::CallbackGroup> callback_group = nullptr

ROS callback group used by the subscriber callbacks.

std::optional<std::chrono::nanoseconds> no_message_timeout = std::nullopt

Time after which timeout callback is called if no message is received.

std::shared_ptr<mrs_lib::TimeoutManager2> timeout_manager = nullptr

Timeout manager used for the no message timeout.

If nullptr and timeout is set, the Subscriber will create its own timeout manager.

std::function<void(std::string_view topic_name, rclcpp::Time last_msg)> timeout_callback = {}

Timeout manager used for the no message timeout.

If not set, a default will be used.

Example

Example node using the mrs_lib::Subscriber.
 1class ExampleNode : public rclcpp::Node
 2{
 3public:
 4  ExampleNode(const rclcpp::NodeOptions& options = rclcpp::NodeOptions{})
 5      : Node("example_node", options),
 6        logger_(*this),
 7        subscriber_(mrs_lib::SubscriberOptions{.node_interfaces = *this}, "example_topic", std::bind_front(&ExampleNode::message_callback, this))
 8  {
 9  }
10
11  [[nodiscard]] int64_t get_last_val() const
12  {
13    return last_val_;
14  }
15
16private:
17  void message_callback(std::shared_ptr<const std_msgs::msg::Int64> msg)
18  {
19    logger_.info("Message received with payload: {}", msg->data);
20    last_val_ = msg->data;
21  }
22
23  mrs_lib::Logger logger_;
24
25  std::atomic<int64_t> last_val_ = 0;
26
27  mrs_lib::Subscriber<std_msgs::msg::Int64> subscriber_;
28};