Stage 2: agnocast::Node

In Stage 2, you replace rclcpp::Node with agnocast::Node. This bypasses the rcl layer entirely — no RMW participant is created — reducing launch time and CPU usage.

Prerequisite

Stage 2 can only be applied to a node once all publishers and subscriptions in that node have been migrated to Agnocast APIs (Stage 1 complete).

Migrating a Publisher

Before (Stage 1)

#include "agnocast/agnocast.hpp"
#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/string.hpp"

class MyPublisher : public rclcpp::Node
{
  agnocast::Publisher<std_msgs::msg::String>::SharedPtr pub_;
  rclcpp::TimerBase::SharedPtr timer_;

  void timer_callback()
  {
    auto msg = pub_->borrow_loaned_message();
    msg->data = "Hello, world!";
    pub_->publish(std::move(msg));
  }

public:
  MyPublisher() : Node("my_publisher")
  {
    auto group = create_callback_group(rclcpp::CallbackGroupType::MutuallyExclusive);

    pub_ = agnocast::create_publisher<std_msgs::msg::String>(
      this, "/topic", 10);
    timer_ = create_wall_timer(100ms,
      std::bind(&MyPublisher::timer_callback, this), group);
  }
};

After (Stage 2)

#include "agnocast/agnocast.hpp"
#include "std_msgs/msg/string.hpp"

class MyPublisher : public agnocast::Node                           // (1)
{
  agnocast::Publisher<std_msgs::msg::String>::SharedPtr pub_;
  agnocast::TimerBase::SharedPtr timer_;                            // (2)

  void timer_callback()
  {
    auto msg = pub_->borrow_loaned_message();
    msg->data = "Hello, world!";
    pub_->publish(std::move(msg));
  }

public:
  MyPublisher() : Node("my_publisher")
  {
    auto group = create_callback_group(rclcpp::CallbackGroupType::MutuallyExclusive);

    pub_ = this->create_publisher<std_msgs::msg::String>(           // (3)
      "/topic", 10);
    timer_ = this->create_wall_timer(100ms,
      std::bind(&MyPublisher::timer_callback, this), group);
  }
};

Key changes:

1. Base class changes from rclcpp::Node to agnocast::Node
2. Timer type changes to agnocast::TimerBase::SharedPtr
3. Publisher creation uses member function this->create_publisher(...) instead of free function

Migrating a Subscription

Before (Stage 1)

#include "agnocast/agnocast.hpp"
#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/string.hpp"

class MySubscriber : public rclcpp::Node
{
  agnocast::Subscription<std_msgs::msg::String>::SharedPtr sub_;

  void callback(const agnocast::ipc_shared_ptr<std_msgs::msg::String> & msg)
  {
    RCLCPP_INFO(get_logger(), "Received: %s", msg->data.c_str());
  }

public:
  MySubscriber() : Node("my_subscriber")
  {
    auto group = create_callback_group(rclcpp::CallbackGroupType::MutuallyExclusive);
    agnocast::SubscriptionOptions options;
    options.callback_group = group;

    sub_ = agnocast::create_subscription<std_msgs::msg::String>(
      this, "/topic", 10,
      std::bind(&MySubscriber::callback, this, std::placeholders::_1),
      options);
  }
};

After (Stage 2)

#include "agnocast/agnocast.hpp"
#include "std_msgs/msg/string.hpp"

class MySubscriber : public agnocast::Node                          // (1)
{
  agnocast::Subscription<std_msgs::msg::String>::SharedPtr sub_;

  void callback(const agnocast::ipc_shared_ptr<std_msgs::msg::String> & msg)
  {
    RCLCPP_INFO(get_logger(), "Received: %s", msg->data.c_str());
  }

public:
  MySubscriber() : Node("my_subscriber")
  {
    auto group = create_callback_group(rclcpp::CallbackGroupType::MutuallyExclusive);
    agnocast::SubscriptionOptions options;
    options.callback_group = group;

    sub_ = this->create_subscription<std_msgs::msg::String>(        // (2)
      "/topic", 10,
      std::bind(&MySubscriber::callback, this, std::placeholders::_1),
      options);
  }
};

Key changes:

1. Base class changes to agnocast::Node
2. Subscription creation uses member function instead of free function

Switching the Executor (Nodes with main)

Replace the initialization and executor.

Before (Stage 1):

int main(int argc, char * argv[])
{
  rclcpp::init(argc, argv);
  agnocast::SingleThreadedAgnocastExecutor executor;
  auto node = std::make_shared<MyNode>();
  executor.add_node(node);
  executor.spin();
  rclcpp::shutdown();
}

After (Stage 2):

int main(int argc, char * argv[])
{
  agnocast::init(argc, argv);                                       // (1)
  agnocast::AgnocastOnlySingleThreadedExecutor executor;            // (2)
  auto node = std::make_shared<MyNode>();
  executor.add_node(node);
  executor.spin();
}

Key changes:

1. rclcpp::init() → agnocast::init(), rclcpp::shutdown() no longer needed
2. Executor changes to AgnocastOnly* variant

Available executors for Stage 2:

Executor
agnocast::AgnocastOnlySingleThreadedExecutor
agnocast::AgnocastOnlyMultiThreadedExecutor
agnocast::AgnocastOnlyCallbackIsolatedExecutor

Note

If a process contains a mix of rclcpp::Node (Stage 1) and agnocast::Node (Stage 2) nodes, use the non-AgnocastOnly executors (e.g., agnocast::CallbackIsolatedAgnocastExecutor), which can handle both.

Switching the Executor (Composable Nodes)

Replace the EXECUTOR option with an AgnocastOnly* variant.

CMakeLists.txt (before — Stage 1):

agnocast_components_register_node(
  my_component
  PLUGIN "MyNode"
  EXECUTABLE my_node
)

CMakeLists.txt (after — Stage 2):

agnocast_components_register_node(
  my_component
  PLUGIN "MyNode"
  EXECUTABLE my_node
  EXECUTOR AgnocastOnlySingleThreadedExecutor
)

No launch file changes are needed from Stage 1 — LD_PRELOAD and the container executable remain the same.

Supplementary Information

agnocast::Node API Compatibility

agnocast::Node provides an API largely compatible with rclcpp::Node, but some APIs are not yet supported. Before migrating to Stage 2, check the agnocast::Node interface comparison to confirm the APIs your node uses are supported.

Summary of Changes from Stage 1 to Stage 2

Aspect	Stage 1	Stage 2
Node class	rclcpp::Node	agnocast::Node
Pub/sub creation	agnocast::create_*(this, ...)	this->create_*(...)
Initialization	rclcpp::init()	agnocast::init()
Executor	agnocast::*AgnocastExecutor	agnocast::AgnocastOnly*Executor
rclcpp dependency	Required	Not required
RMW participant	Created	Not created