ROS2机器人编程简述humble-第二章-Controlling the Iterative Execution .3.1

2.3 ANALYZING THE BR2 BASICS PACKAGE 这一节内容有些多……

前一篇：

ROS2机器人编程简述humble-第二章-DEVELOPING THE FIRST NODE .2

里面只有节点，没有任何实际功能。

logger.cpp代码如下所示：

#include "rclcpp/rclcpp.hpp"

using namespace std::chrono_literals;

int main(int argc, char * argv[])
{
  rclcpp::init(argc, argv);

  auto node = rclcpp::Node::make_shared("logger_node");

  rclcpp::Rate loop_rate(500ms);
  int counter = 0;
  while (rclcpp::ok()) {
    RCLCPP_INFO(node->get_logger(), "Hello %d", counter++);

    rclcpp::spin_some(node);
    loop_rate.sleep();
  }

  rclcpp::shutdown();
  return 0;
}

这是一段代码“实现在固定时间执行任务“

周期：rclcpp::Rate loop_rate(500ms);

消息：RCLCPP_INFO(node->get_logger(), "Hello %d", counter++);

ROS消息通常具备时间戳！

rclcpp::spin_some(node);

参考官方文档如下：

rclcpp::spin

Create a default single-threaded executor and spin the specified node.

创建默认的单线程执行器并跳转指定的节点。

rclcpp::spin_some

Create a default single-threaded executor and execute any immediately available work.

创建默认的单线程执行器并执行任何立即可用的工作。

rclcpp::spin_until_future_complete

rcl_interfaces/msg/Log.msg

# Debug is for pedantic information, which is useful when debugging issues. byte DEBUG=10 # Info is the standard informational level and is used to report expected # information. byte INFO=20 # Warning is for information that may potentially cause issues or possibly unexpected # behavior. byte WARN=30 # Error is for information that this node cannot resolve. byte ERROR=40 # Information about a impending node shutdown. byte FATAL=50 # # Fields # # Timestamp when this message was generated by the node. builtin_interfaces/Time stamp # Corresponding log level, see above definitions. uint8 level # The name representing the logger this message came from. string name # The full log message. string msg # The file the message came from. string file # The function the message came from. string function # The line in the file the message came from. uint32 line

重要图示：

ros2 run br2_basics logger

ros2 topic echo /rosout

ros2 interface show rcl_interfaces/msg/Log

另一种实现方法：

#include "rclcpp/rclcpp.hpp"

using namespace std::chrono_literals;

class LoggerNode : public rclcpp::Node
{
public:
  LoggerNode()
  : Node("logger_node")
  {
    counter_ = 0;
    timer_ = create_wall_timer(
      500ms, std::bind(&LoggerNode::timer_callback, this));
  }

  void timer_callback()
  {
    RCLCPP_INFO(get_logger(), "Hello %d", counter_++);
  }

private:
  rclcpp::TimerBase::SharedPtr timer_;
  int counter_;
};

int main(int argc, char * argv[])
{
  rclcpp::init(argc, argv);

  auto node = std::make_shared<LoggerNode>();

  rclcpp::spin(node);

  rclcpp::shutdown();
  return 0;
}

计时器控制控制回路。该计时器以所需频率产生事件。当发生此事件时，它调用处理它的回调。优点是节点在内部调整执行频率，而不将此决定委托给外部代码。安排节点以了解它们的运行频率。

timer_ = create_wall_timer(

500ms, std::bind(&LoggerNode::timer_callback, this));

rclcpp: ROS Client Library for C++

rclcpp provides the canonical C++ API for interacting with ROS. It consists of these main components:

Node

rclcpp::Node

rclcpp/node.hpp

Publisher

rclcpp::Node::create_publisher()

rclcpp::Publisher

rclcpp::Publisher::publish()

rclcpp/publisher.hpp

Subscription

rclcpp::Node::create_subscription()

rclcpp::Subscription

rclcpp/subscription.hpp

Service Client

rclcpp::Node::create_client()

rclcpp::Client

rclcpp/client.hpp

Service Server

rclcpp::Node::create_service()

rclcpp::Service

rclcpp/service.hpp

Timer

rclcpp::Node::create_wall_timer()

rclcpp::WallTimer

rclcpp::TimerBase

rclcpp/timer.hpp

Parameters:

rclcpp::Node::set_parameters()

rclcpp::Node::get_parameters()

rclcpp::Node::get_parameter()

rclcpp::Node::describe_parameters()

rclcpp::Node::list_parameters()

rclcpp::Node::add_on_set_parameters_callback()

rclcpp::Node::remove_on_set_parameters_callback()

rclcpp::Parameter

rclcpp::ParameterValue

rclcpp::AsyncParametersClient

rclcpp::SyncParametersClient

rclcpp/parameter.hpp

rclcpp/parameter_value.hpp

rclcpp/parameter_client.hpp

rclcpp/parameter_service.hpp

Rate:

rclcpp::Rate

rclcpp::WallRate

rclcpp/rate.hpp

There are also some components which help control the execution of callbacks:

Executors (responsible for execution of callbacks through a blocking spin):

rclcpp::spin()

rclcpp::spin_some()

rclcpp::spin_until_future_complete()

rclcpp::executors::SingleThreadedExecutor

rclcpp::executors::SingleThreadedExecutor::add_node()

rclcpp::executors::SingleThreadedExecutor::spin()

rclcpp::executors::MultiThreadedExecutor

rclcpp::executors::MultiThreadedExecutor::add_node()

rclcpp::executors::MultiThreadedExecutor::spin()

rclcpp/executor.hpp

rclcpp/executors.hpp

rclcpp/executors/single_threaded_executor.hpp

rclcpp/executors/multi_threaded_executor.hpp

CallbackGroups (mechanism for enforcing concurrency rules for callbacks):

rclcpp::Node::create_callback_group()

rclcpp::CallbackGroup

rclcpp/callback_group.hpp

Additionally, there are some methods for introspecting the ROS graph:

Graph Events (a waitable event object that wakes up when the graph changes):

rclcpp::Node::get_graph_event()

rclcpp::Node::wait_for_graph_change()

rclcpp::Event

List topic names and types:

rclcpp::Node::get_topic_names_and_types()

Get the number of publishers or subscribers on a topic:

rclcpp::Node::count_publishers()

rclcpp::Node::count_subscribers()

And components related to logging:

Logging macros:

Some examples (not exhaustive):

RCLCPP_DEBUG()

RCLCPP_INFO()

RCLCPP_WARN_ONCE()

RCLCPP_ERROR_SKIPFIRST()

rclcpp/logging.hpp

Logger:

rclcpp::Logger

rclcpp/logger.hpp

rclcpp::Node::get_logger()

Finally, there are many internal API's and utilities:

Exceptions:

rclcpp/exceptions.hpp

Allocator related items:

rclcpp/allocator/allocator_common.hpp

rclcpp/allocator/allocator_deleter.hpp

Memory management tools:

rclcpp/memory_strategies.hpp

rclcpp/memory_strategy.hpp

rclcpp/message_memory_strategy.hpp

rclcpp/strategies/allocator_memory_strategy.hpp

rclcpp/strategies/message_pool_memory_strategy.hpp

Context object which is shared amongst multiple Nodes:

rclcpp::Context

rclcpp/context.hpp

rclcpp/contexts/default_context.hpp

Various utilities:

rclcpp/duration.hpp

rclcpp/function_traits.hpp

rclcpp/macros.hpp

rclcpp/scope_exit.hpp

rclcpp/time.hpp

rclcpp/utilities.hpp

rclcpp/visibility_control.hpp