【机器人】ROS1工程案例：服务和动作

我们这一部分模拟一个低能的阶乘计算器，来比较Service和Action的差异。

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本系列用时9天，博主也是从零开始，尽力去写的，如果发现了错误一定要私信告诉我呀。这么努力的博主，关注一下吧。

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:star:案例目标

说明以下问题

• ROS中message，action，service的定义方式大同小异。
• 在消息作为一等公民的ROS软件中，灵活使用面向对象思想。
• 文件的命名问题，很多文件的命名是很有讲究的，节点名也是。
• ROS使用大量多线程并行的思想，需要理解并行与并发、python的主锁以及阻塞和上锁的区别。

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:star:准备工作

• 基础步骤参见：【机器人】ROS程序框架：架构部分
• 创建factorial_calculator包

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:star:服务部分

:sparkles:定义文件

创建一个名为FactorialService.srv，定义输入和输出

uint32 num_in
--- 
uint32 num_out

取消package.xml中的注释

添加信息到CMakeLists.txt

find_package(catkin REQUIRED COMPONENTS
  rospy
  std_msgs # 新增
  message_generation # 新增
)

# Generate services in the 'srv' folder
add_service_files(
  FILES
  FactorialService.srv # 新增
)

取消CMakeLists.txt中的注释

使用$catkin_make编译

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:sparkles:使用服务

客户端factorial_service_client.py代码

#!/usr/bin/env python3

import rospy
from factorial_calculator.srv import FactorialService 

class FactorialServiceClient():
    def __init__(self):
        rospy.init_node('service_client_factorial')
        rospy.wait_for_service('service/server/factorial/service')
        self.factorise = rospy.ServiceProxy('service/server/factorial/service', FactorialService)
    
    def call(self,num):
        return self.factorise(num).num_out


if __name__ == '__main__':
    client = FactorialServiceClient()
    while input_num := input("Input a num: "):
        if not input_num.isdigit():
            continue
        input_num = int(input_num)
        result = client.call(input_num)
        print(f"Result is: {result}")

服务端factorial_service_server.py代码

#!/usr/bin/env python3

import rospy
from factorial_calculator.srv import FactorialService,FactorialServiceResponse

class FactorialServiceServer():
    def __init__(self):
        rospy.init_node('service_server_factorial')

    def factorise(self,num):
        result = 1
        for i in range(1,num+1):
            result *= i
            rospy.sleep(0.2)
            print(result)
        return result
    
    def run(self):
        service = rospy.Service('service/server/factorial/service', FactorialService, lambda x : FactorialServiceResponse(self.factorise(x.num_in)))
        rospy.spin()
        
if __name__ == '__main__':
    server = FactorialServiceServer()
    server.run()

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:sparkles:效果

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:star:动作部分

:sparkles:定义文件

创建一个名为FactorialAction.action

uint32 num_in
---
uint32 num_process
--- 
uint32 num_out

在package.xml添加信息

<build_depend>actionlib_msgs</build_depend>
<exec_depend>actionlib_msgs</exec_depend>

CMakeLists.txt

# Generate actions in the 'action' folder
add_action_files(
  FILES
  FactorialAction.action # 新增
)

添加actionlib_msgs依赖

find_package(catkin REQUIRED COMPONENTS
  rospy
  std_msgs
  actionlib_msgs # 新增
  message_generation
)

generate_messages(
  DEPENDENCIES
  std_msgs  # Or other packages containing msgs
  actionlib_msgs # 新增
)

catkin_package(
#  INCLUDE_DIRS include
#  LIBRARIES factorial_calculator
#  CATKIN_DEPENDS rospy
#  DEPENDS system_lib
  actionlib_msgs # 新增
)

$catkin_make

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:sparkles:使用服务

客户端factorial_action_client.py代码

#!/usr/bin/env python3

import rospy

import actionlib
from factorial_calculator.msg import FactorialActionAction,FactorialActionGoal,FactorialActionResult

class FactorialActionClient():
    def __init__(self):
        # 初始化节点
        rospy.init_node('action_client_factorial')
        
        # 定义动作客户端
        self.client = actionlib.SimpleActionClient('action/server/factorial/action',
                                                   FactorialActionAction)
        self.client.wait_for_server()
          
    def feedback_callback(self,feedback):
        if int(feedback)>100000:
            self.client.cancel_goal()
        print('Feedback:', feedback)
    
    def call(self,num):
        # 定义goal
        goal = FactorialActionGoal()
        goal.num_goal = num
        
        # 发送goal
        self.client.send_goal(goal, feedback_cb=lambda x : self.feedback_callback(x.num_feedback))
        
        # 阻塞等待结果，一般是不会这样使用的
        # 这是多线程中的阻塞步骤
        self.client.wait_for_result()
        return self.client.get_result().num_result


if __name__ == '__main__':
    client = FactorialActionClient()

    # 循环读取终端输入并上传动作服务器执行。
    while input_num := input("Input a num: "):
        if not input_num.isdigit():
            continue
        input_num = int(input_num)
        result = client.call(input_num)
        print(f"Result is: {result}")

服务端factorial_action_server.py代码

#!/usr/bin/env python3

import rospy

import actionlib
from factorial_calculator.msg import FactorialActionAction,FactorialActionGoal,FactorialActionResult,FactorialActionFeedback

class FactorialActionServer():
    def __init__(self):
        rospy.init_node('action_server_factorial')
        self.server = actionlib.SimpleActionServer('action/server/factorial/action', 
                                            FactorialActionAction,
                                            lambda x : self.factorise(x.num_goal),
                                            auto_start=False)

    def factorise(self,num):
        result = 1
        
        if num > 14:
            self.server.set_aborted(FactorialActionResult(result),'[aborted]')
            return
        
        for i in range(1,num+1):
            
            if self.server.is_preempt_requested():
                self.server.set_preempted(FactorialActionResult(result),'[preempted]')
                
            result *= i
            rospy.sleep(0.2)
            self.server.publish_feedback(FactorialActionFeedback(result))
            
        self.server.set_succeeded(FactorialActionResult(result))
        return 
    
    def run(self):
        self.server.start()
        rospy.spin()
        
if __name__ == '__main__':
    server = FactorialActionServer()
    server.run()

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:sparkles:效果