实现 action 服务器和客户端(C++)
目标: 在 C++ 中实现 action 服务器和客户端。
教程等级: 中级
预计时长: 15 分钟
背景
Actions 是 ROS 2 中的一种异步通信形式。 Action 客户端 发送目标请求到 Action 服务器。 Action 服务器 发送目标反馈和结果到 Action 客户端。
前提条件
你需要有 action_tutorials_interfaces
包和在之前的教程 创建 action 中定义的 Fibonacci.action
接口。
任务
1 创建 action_tutorials_cpp 包
正如我们在 创建 ROS 2 包 教程中看到的,我们需要创建一个新的包来保存 C++ 和相关代码。
1.1 创建 action_tutorials_cpp 包
进入你在 上一个教程 中创建的 action 工作空间(记得 source 这个工作空间),并为 C++ action 服务器创建一个新的包:
cd ~/ros2_ws/src
ros2 pkg create --dependencies action_tutorials_interfaces rclcpp rclcpp_action rclcpp_components -- action_tutorials_cpp
cd ~/ros2_ws/src
ros2 pkg create --dependencies action_tutorials_interfaces rclcpp rclcpp_action rclcpp_components -- action_tutorials_cpp
cd \dev\ros2_ws\src
ros2 pkg create --dependencies action_tutorials_interfaces rclcpp rclcpp_action rclcpp_components -- action_tutorials_cpp
1.2 添加可见性控制
为了使包能够在 Windows 上编译和工作,我们需要添加一些 “可见性控制”。 有关更多详细信息,请参见 Windows Tips and Tricks 文档中的 Windows Symbol Visibility。
打开 action_tutorials_cpp/include/action_tutorials_cpp/visibility_control.h
,并添加以下代码:
#ifndef ACTION_TUTORIALS_CPP__VISIBILITY_CONTROL_H_
#define ACTION_TUTORIALS_CPP__VISIBILITY_CONTROL_H_
#ifdef __cplusplus
extern "C"
{
#endif
// This logic was borrowed (then namespaced) from the examples on the gcc wiki:
// https://gcc.gnu.org/wiki/Visibility
#if defined _WIN32 || defined __CYGWIN__
#ifdef __GNUC__
#define ACTION_TUTORIALS_CPP_EXPORT __attribute__ ((dllexport))
#define ACTION_TUTORIALS_CPP_IMPORT __attribute__ ((dllimport))
#else
#define ACTION_TUTORIALS_CPP_EXPORT __declspec(dllexport)
#define ACTION_TUTORIALS_CPP_IMPORT __declspec(dllimport)
#endif
#ifdef ACTION_TUTORIALS_CPP_BUILDING_DLL
#define ACTION_TUTORIALS_CPP_PUBLIC ACTION_TUTORIALS_CPP_EXPORT
#else
#define ACTION_TUTORIALS_CPP_PUBLIC ACTION_TUTORIALS_CPP_IMPORT
#endif
#define ACTION_TUTORIALS_CPP_PUBLIC_TYPE ACTION_TUTORIALS_CPP_PUBLIC
#define ACTION_TUTORIALS_CPP_LOCAL
#else
#define ACTION_TUTORIALS_CPP_EXPORT __attribute__ ((visibility("default")))
#define ACTION_TUTORIALS_CPP_IMPORT
#if __GNUC__ >= 4
#define ACTION_TUTORIALS_CPP_PUBLIC __attribute__ ((visibility("default")))
#define ACTION_TUTORIALS_CPP_LOCAL __attribute__ ((visibility("hidden")))
#else
#define ACTION_TUTORIALS_CPP_PUBLIC
#define ACTION_TUTORIALS_CPP_LOCAL
#endif
#define ACTION_TUTORIALS_CPP_PUBLIC_TYPE
#endif
#ifdef __cplusplus
}
#endif
#endif // ACTION_TUTORIALS_CPP__VISIBILITY_CONTROL_H_
1.3 编写 action 服务器
让我们专注实现一个计算斐波那契数列的 action 服务器,会用到在 创建 action 教程中创建的 action 。
2.1 编写 action 服务器代码
打开 action_tutorials_cpp/src/fibonacci_action_server.cpp
,并添加以下代码:
#include <functional>
#include <memory>
#include <thread>
#include "action_tutorials_interfaces/action/fibonacci.hpp"
#include "rclcpp/rclcpp.hpp"
#include "rclcpp_action/rclcpp_action.hpp"
#include "rclcpp_components/register_node_macro.hpp"
#include "action_tutorials_cpp/visibility_control.h"
namespace action_tutorials_cpp
{
class FibonacciActionServer : public rclcpp::Node
{
public:
using Fibonacci = action_tutorials_interfaces::action::Fibonacci;
using GoalHandleFibonacci = rclcpp_action::ServerGoalHandle<Fibonacci>;
ACTION_TUTORIALS_CPP_PUBLIC
explicit FibonacciActionServer(const rclcpp::NodeOptions & options = rclcpp::NodeOptions())
: Node("fibonacci_action_server", options)
{
using namespace std::placeholders;
this->action_server_ = rclcpp_action::create_server<Fibonacci>(
this,
"fibonacci",
std::bind(&FibonacciActionServer::handle_goal, this, _1, _2),
std::bind(&FibonacciActionServer::handle_cancel, this, _1),
std::bind(&FibonacciActionServer::handle_accepted, this, _1));
}
private:
rclcpp_action::Server<Fibonacci>::SharedPtr action_server_;
rclcpp_action::GoalResponse handle_goal(
const rclcpp_action::GoalUUID & uuid,
std::shared_ptr<const Fibonacci::Goal> goal)
{
RCLCPP_INFO(this->get_logger(), "Received goal request with order %d", goal->order);
(void)uuid;
return rclcpp_action::GoalResponse::ACCEPT_AND_EXECUTE;
}
rclcpp_action::CancelResponse handle_cancel(
const std::shared_ptr<GoalHandleFibonacci> goal_handle)
{
RCLCPP_INFO(this->get_logger(), "Received request to cancel goal");
(void)goal_handle;
return rclcpp_action::CancelResponse::ACCEPT;
}
void handle_accepted(const std::shared_ptr<GoalHandleFibonacci> goal_handle)
{
using namespace std::placeholders;
// this needs to return quickly to avoid blocking the executor, so spin up a new thread
std::thread{std::bind(&FibonacciActionServer::execute, this, _1), goal_handle}.detach();
}
void execute(const std::shared_ptr<GoalHandleFibonacci> goal_handle)
{
RCLCPP_INFO(this->get_logger(), "Executing goal");
rclcpp::Rate loop_rate(1);
const auto goal = goal_handle->get_goal();
auto feedback = std::make_shared<Fibonacci::Feedback>();
auto & sequence = feedback->partial_sequence;
sequence.push_back(0);
sequence.push_back(1);
auto result = std::make_shared<Fibonacci::Result>();
for (int i = 1; (i < goal->order) && rclcpp::ok(); ++i) {
// Check if there is a cancel request
if (goal_handle->is_canceling()) {
result->sequence = sequence;
goal_handle->canceled(result);
RCLCPP_INFO(this->get_logger(), "Goal canceled");
return;
}
// Update sequence
sequence.push_back(sequence[i] + sequence[i - 1]);
// Publish feedback
goal_handle->publish_feedback(feedback);
RCLCPP_INFO(this->get_logger(), "Publish feedback");
loop_rate.sleep();
}
// Check if goal is done
if (rclcpp::ok()) {
result->sequence = sequence;
goal_handle->succeed(result);
RCLCPP_INFO(this->get_logger(), "Goal succeeded");
}
}
}; // class FibonacciActionServer
} // namespace action_tutorials_cpp
RCLCPP_COMPONENTS_REGISTER_NODE(action_tutorials_cpp::FibonacciActionServer)
前几行包含了我们编译所需的所有头文件。
接下来创建一个 rclcpp::Node
的子类:
class FibonacciActionServer : public rclcpp::Node
FibonacciActionServer
构造函数将节点名称初始化为 fibonacci_action_server
:
explicit FibonacciActionServer(const rclcpp::NodeOptions & options = rclcpp::NodeOptions())
: Node("fibonacci_action_server", options)
构造函数还实例化了一个新的 action 服务器:
this->action_server_ = rclcpp_action::create_server<Fibonacci>(
this,
"fibonacci",
std::bind(&FibonacciActionServer::handle_goal, this, _1, _2),
std::bind(&FibonacciActionServer::handle_cancel, this, _1),
std::bind(&FibonacciActionServer::handle_accepted, this, _1));
一个 action 服务器需要 6 个信息:
action 类型名称:
Fibonacci
。一个 action 所属的 ROS 2 节点:
this
。action 名称:
'fibonacci'
。用于处理目标的回调函数:
handle_goal
。用于处理取消的回调函数:
handle_cancel
。用于处理目标接受的回调函数:
handle_accept
。
接下来是文件中的几个回调的实现。 注意,所有回调都需要快速返回,否则可能会导致 executor 闲置。
我们从处理新目标的回调开始:
rclcpp_action::GoalResponse handle_goal(
const rclcpp_action::GoalUUID & uuid,
std::shared_ptr<const Fibonacci::Goal> goal)
{
RCLCPP_INFO(this->get_logger(), "Received goal request with order %d", goal->order);
(void)uuid;
return rclcpp_action::GoalResponse::ACCEPT_AND_EXECUTE;
}
目前这个实现直接接受所有目标。
接下来是处理取消的回调:
rclcpp_action::CancelResponse handle_cancel(
const std::shared_ptr<GoalHandleFibonacci> goal_handle)
{
RCLCPP_INFO(this->get_logger(), "Received request to cancel goal");
(void)goal_handle;
return rclcpp_action::CancelResponse::ACCEPT;
}
目前这个实现只告诉客户端它接受了取消请求。
最后一个回调用于接受一个新目标并开始处理:
void handle_accepted(const std::shared_ptr<GoalHandleFibonacci> goal_handle)
{
using namespace std::placeholders;
// this needs to return quickly to avoid blocking the executor, so spin up a new thread
std::thread{std::bind(&FibonacciActionServer::execute, this, _1), goal_handle}.detach();
}
由于执行是一个长时间运行的操作,我们创建一个线程来执行实际的工作,并快速从 handle_accepted
返回。
所有进一步的处理和更新都在新线程的 execute
方法中完成:
void execute(const std::shared_ptr<GoalHandleFibonacci> goal_handle)
{
RCLCPP_INFO(this->get_logger(), "Executing goal");
rclcpp::Rate loop_rate(1);
const auto goal = goal_handle->get_goal();
auto feedback = std::make_shared<Fibonacci::Feedback>();
auto & sequence = feedback->partial_sequence;
sequence.push_back(0);
sequence.push_back(1);
auto result = std::make_shared<Fibonacci::Result>();
for (int i = 1; (i < goal->order) && rclcpp::ok(); ++i) {
// Check if there is a cancel request
if (goal_handle->is_canceling()) {
result->sequence = sequence;
goal_handle->canceled(result);
RCLCPP_INFO(this->get_logger(), "Goal canceled");
return;
}
// Update sequence
sequence.push_back(sequence[i] + sequence[i - 1]);
// Publish feedback
goal_handle->publish_feedback(feedback);
RCLCPP_INFO(this->get_logger(), "Publish feedback");
loop_rate.sleep();
}
// Check if goal is done
if (rclcpp::ok()) {
result->sequence = sequence;
goal_handle->succeed(result);
RCLCPP_INFO(this->get_logger(), "Goal succeeded");
}
}
这个工作线程每秒处理一个斐波那契数列的序列号,为每一步发布一个反馈更新。
当处理完成时,它将 goal_handle
标记为成功,并退出。
现在我们有了功能完整的 action 服务器。让我们构建并运行它。
2.2 构建 action 服务器
在上一节中,我们准备好了 action 服务器的代码。 我们还需要做一些额外的事情,才能构建和运行它。
首先,我们需要设置 CMakeLists.txt,来确保能够构建 action 服务器。
打开 action_tutorials_cpp/CMakeLists.txt
,并在 find_package
之后添加以下内容:
add_library(action_server SHARED
src/fibonacci_action_server.cpp)
target_include_directories(action_server PRIVATE
$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
$<INSTALL_INTERFACE:include>)
target_compile_definitions(action_server
PRIVATE "ACTION_TUTORIALS_CPP_BUILDING_DLL")
ament_target_dependencies(action_server
"action_tutorials_interfaces"
"rclcpp"
"rclcpp_action"
"rclcpp_components")
rclcpp_components_register_node(action_server PLUGIN "action_tutorials_cpp::FibonacciActionServer" EXECUTABLE fibonacci_action_server)
install(TARGETS
action_server
ARCHIVE DESTINATION lib
LIBRARY DESTINATION lib
RUNTIME DESTINATION bin)
现在我们可以构建包了。进入 ros2_ws
的顶层目录,并运行:
colcon build
这将构建整个工作空间,包括 action_tutorials_cpp
包中的 fibonacci_action_server
。
2.3 运行 action 服务器
现在已经有了编译好的 action 服务器,可以运行它了。
Source 刚刚构建的工作空间(ros2_ws
),并运行 action 服务器:
ros2 run action_tutorials_cpp fibonacci_action_server
3 编写 action 客户端
3.1 编写 action 客户端代码
打开 action_tutorials_cpp/src/fibonacci_action_client.cpp
,并添加以下代码:
#include <functional>
#include <future>
#include <memory>
#include <string>
#include <sstream>
#include "action_tutorials_interfaces/action/fibonacci.hpp"
#include "rclcpp/rclcpp.hpp"
#include "rclcpp_action/rclcpp_action.hpp"
#include "rclcpp_components/register_node_macro.hpp"
namespace action_tutorials_cpp
{
class FibonacciActionClient : public rclcpp::Node
{
public:
using Fibonacci = action_tutorials_interfaces::action::Fibonacci;
using GoalHandleFibonacci = rclcpp_action::ClientGoalHandle<Fibonacci>;
explicit FibonacciActionClient(const rclcpp::NodeOptions & options)
: Node("fibonacci_action_client", options)
{
this->client_ptr_ = rclcpp_action::create_client<Fibonacci>(
this,
"fibonacci");
this->timer_ = this->create_wall_timer(
std::chrono::milliseconds(500),
std::bind(&FibonacciActionClient::send_goal, this));
}
void send_goal()
{
using namespace std::placeholders;
this->timer_->cancel();
if (!this->client_ptr_->wait_for_action_server()) {
RCLCPP_ERROR(this->get_logger(), "Action server not available after waiting");
rclcpp::shutdown();
}
auto goal_msg = Fibonacci::Goal();
goal_msg.order = 10;
RCLCPP_INFO(this->get_logger(), "Sending goal");
auto send_goal_options = rclcpp_action::Client<Fibonacci>::SendGoalOptions();
send_goal_options.goal_response_callback =
std::bind(&FibonacciActionClient::goal_response_callback, this, _1);
send_goal_options.feedback_callback =
std::bind(&FibonacciActionClient::feedback_callback, this, _1, _2);
send_goal_options.result_callback =
std::bind(&FibonacciActionClient::result_callback, this, _1);
this->client_ptr_->async_send_goal(goal_msg, send_goal_options);
}
private:
rclcpp_action::Client<Fibonacci>::SharedPtr client_ptr_;
rclcpp::TimerBase::SharedPtr timer_;
void goal_response_callback(const GoalHandleFibonacci::SharedPtr & goal_handle)
{
if (!goal_handle) {
RCLCPP_ERROR(this->get_logger(), "Goal was rejected by server");
} else {
RCLCPP_INFO(this->get_logger(), "Goal accepted by server, waiting for result");
}
}
void feedback_callback(
GoalHandleFibonacci::SharedPtr,
const std::shared_ptr<const Fibonacci::Feedback> feedback)
{
std::stringstream ss;
ss << "Next number in sequence received: ";
for (auto number : feedback->partial_sequence) {
ss << number << " ";
}
RCLCPP_INFO(this->get_logger(), ss.str().c_str());
}
void result_callback(const GoalHandleFibonacci::WrappedResult & result)
{
switch (result.code) {
case rclcpp_action::ResultCode::SUCCEEDED:
break;
case rclcpp_action::ResultCode::ABORTED:
RCLCPP_ERROR(this->get_logger(), "Goal was aborted");
return;
case rclcpp_action::ResultCode::CANCELED:
RCLCPP_ERROR(this->get_logger(), "Goal was canceled");
return;
default:
RCLCPP_ERROR(this->get_logger(), "Unknown result code");
return;
}
std::stringstream ss;
ss << "Result received: ";
for (auto number : result.result->sequence) {
ss << number << " ";
}
RCLCPP_INFO(this->get_logger(), ss.str().c_str());
rclcpp::shutdown();
}
}; // class FibonacciActionClient
} // namespace action_tutorials_cpp
RCLCPP_COMPONENTS_REGISTER_NODE(action_tutorials_cpp::FibonacciActionClient)
前几行包含了我们编译所需的所有头文件。
接下来创建一个 rclcpp::Node
的子类:
class FibonacciActionClient : public rclcpp::Node
FibonacciActionClient
构造函数将节点名称初始化为 fibonacci_action_client
:
explicit FibonacciActionClient(const rclcpp::NodeOptions & options)
: Node("fibonacci_action_client", options)
构造函数还实例化了一个新的 action 客户端:
this->client_ptr_ = rclcpp_action::create_client<Fibonacci>(
this,
"fibonacci");
一个 action 客户端需要 3 个信息:
action 类型名称:
Fibonacci
。一个 action 所属的 ROS 2 节点:
this
。action 名称:
'fibonacci'
。
我们还实例化了一个 ROS 定时器,它将周期性地调用 send_goal
:
this->timer_ = this->create_wall_timer(
std::chrono::milliseconds(500),
std::bind(&FibonacciActionClient::send_goal, this));
每当定时器到期触发,它都会调用 send_goal
:
void send_goal()
{
using namespace std::placeholders;
this->timer_->cancel();
if (!this->client_ptr_->wait_for_action_server()) {
RCLCPP_ERROR(this->get_logger(), "Action server not available after waiting");
rclcpp::shutdown();
}
auto goal_msg = Fibonacci::Goal();
goal_msg.order = 10;
RCLCPP_INFO(this->get_logger(), "Sending goal");
auto send_goal_options = rclcpp_action::Client<Fibonacci>::SendGoalOptions();
send_goal_options.goal_response_callback =
std::bind(&FibonacciActionClient::goal_response_callback, this, _1);
send_goal_options.feedback_callback =
std::bind(&FibonacciActionClient::feedback_callback, this, _1, _2);
send_goal_options.result_callback =
std::bind(&FibonacciActionClient::result_callback, this, _1);
this->client_ptr_->async_send_goal(goal_msg, send_goal_options);
}
这个函数做了以下事情:
取消定时器(这样它只会被调用一次)。
等待 action 服务器启动。
实例化一个新的
Fibonacci::Goal
。设置响应、反馈以及结果的回调。
发送目标到服务器。
当服务器接收并接受目标时,它会向客户端返回一个响应。
这个响应由 goal_response_callback
处理:
void goal_response_callback(const GoalHandleFibonacci::SharedPtr & goal_handle)
{
if (!goal_handle) {
RCLCPP_ERROR(this->get_logger(), "Goal was rejected by server");
} else {
RCLCPP_INFO(this->get_logger(), "Goal accepted by server, waiting for result");
}
}
假设服务器接受了目标,它就会开始处理。
所有回到客户端的反馈都由 feedback_callback
处理:
void feedback_callback(
GoalHandleFibonacci::SharedPtr,
const std::shared_ptr<const Fibonacci::Feedback> feedback)
{
std::stringstream ss;
ss << "Next number in sequence received: ";
for (auto number : feedback->partial_sequence) {
ss << number << " ";
}
RCLCPP_INFO(this->get_logger(), ss.str().c_str());
}
服务器处理完成后,会向客户端返回一个结果。
这个结果由 result_callback
处理:
void result_callback(const GoalHandleFibonacci::WrappedResult & result)
{
switch (result.code) {
case rclcpp_action::ResultCode::SUCCEEDED:
break;
case rclcpp_action::ResultCode::ABORTED:
RCLCPP_ERROR(this->get_logger(), "Goal was aborted");
return;
case rclcpp_action::ResultCode::CANCELED:
RCLCPP_ERROR(this->get_logger(), "Goal was canceled");
return;
default:
RCLCPP_ERROR(this->get_logger(), "Unknown result code");
return;
}
std::stringstream ss;
ss << "Result received: ";
for (auto number : result.result->sequence) {
ss << number << " ";
}
RCLCPP_INFO(this->get_logger(), ss.str().c_str());
rclcpp::shutdown();
}
}; // class FibonacciActionClient
现在我们有了一个功能完全的 action 客户端。让我们构建并运行它。
3.2 构建 action 客户端
在上一节中,我们准备好了 action 客户端的代码。
我们还需要再做一些额外的事情,才能构建和运行它。
首先,我们需要设置 CMakeLists.txt,以便编译 action 客户端。
打开 action_tutorials_cpp/CMakeLists.txt
,并在 find_package
之后添加以下内容:
add_library(action_client SHARED
src/fibonacci_action_client.cpp)
target_include_directories(action_client PRIVATE
$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
$<INSTALL_INTERFACE:include>)
target_compile_definitions(action_client
PRIVATE "ACTION_TUTORIALS_CPP_BUILDING_DLL")
ament_target_dependencies(action_client
"action_tutorials_interfaces"
"rclcpp"
"rclcpp_action"
"rclcpp_components")
rclcpp_components_register_node(action_client PLUGIN "action_tutorials_cpp::FibonacciActionClient" EXECUTABLE fibonacci_action_client)
install(TARGETS
action_client
ARCHIVE DESTINATION lib
LIBRARY DESTINATION lib
RUNTIME DESTINATION bin)
现在我们可以构建包了。进入 ros2_ws
的顶层目录,并运行:
colcon build
这会构建整个工作空间,包括 action_tutorials_cpp
包中的 fibonacci_action_client
。
3.3 运行 action 客户端
现在我们已经构建了 action 客户端,可以运行它了。
首先确保在另一个终端中运行着一个 action 服务器。
现在 source 我们刚刚构建的工作空间(ros2_ws
),并尝试运行 action 客户端:
ros2 run action_tutorials_cpp fibonacci_action_client
应该能在终端中看到 action 客户端的输出,包括被接受的情况、反馈和结果。
总结
在本教程中,你逐行编写了一个 C++ action 服务器和 action 客户端,并配置它们传递目标、反馈和结果。
相关内容
有多种方法可以在 C++ 中编写 action 服务器和客户端;请查看 ros2/examples 中的
minimal_action_server
andminimal_action_client
.有关 ROS actions 的更详细信息,请参阅 design article。