① 背景
当节点使用服务进行通信时,发送数据请求的节点称为客户机节点,响应请求的节点称为服务节点。请求和响应的结构由.srv文件决定。
这里使用的示例是一个简单的整数加法系统;一个节点请求两个整数的和,另一个节点用结果响应。这儿用python写的
其实简单得功能函数就可以解决了,这个解决了数据交互的问题,比如服务端返回客户端需要的,但是不用在客户端管理的数据或者状态,还是模块化
② 前提
学会创建工作空间和包
③ 任务
Ⅰ 创建一个包
打开终端,准备好环境,切换到dev_ws/src 路径下来创建包
ros2 pkg create --build-type ament_python py_srvcli --dependencies rclpy example_interfaces
然后出一个文件夹
utry@utry:~/dev_ws/src$ tree py_srvcli/
py_srvcli/
├── package.xml
├── py_srvcli
│ └── __init__.py
├── resource
│ └── py_srvcli
├── setup.cfg
├── setup.py
└── test
├── test_copyright.py
├── test_flake8.py
└── test_pep257.py
3 directories, 8 files
加了--dependencies rclcpp example_interfaces
之后,创建包的时候,会自动把package.xml
和CMakeLists.txt
依赖加上,省事,example_interfaces
包含例子srv
文件
utry@utry:~/dev_ws/src/cpp_srvcli$ ros2 interface show example_interfaces/
example_interfaces/action/Fibonacci example_interfaces/srv/AddTwoInts
utry@utry:~/dev_ws/src/cpp_srvcli$ ros2 interface show example_interfaces/srv/AddTwoInts
int64 a
int64 b
---
int64 sum
修改 package.xml
这三个部分还是要改一下的,依赖已经在创建的时候解决了,所以,不用关心依赖了
<description>Python client server tutorial</description>
<maintainer email="you@email.com">Your Name</maintainer>
<license>Apache License 2.0</license>
修改 setup.py
maintainer='Your Name',
maintainer_email='you@email.com',
description='Python client server tutorial',
license='Apache License 2.0',
Ⅱ 写服务节点
到 dev_ws/src/py_srvcli/py_srvcli
下新建文件service_member_function.py
demo 代码:
from example_interfaces.srv import AddTwoInts
import rclpy
from rclpy.node import Node
class MinimalService(Node):
def __init__(self):
super().__init__('minimal_service')
self.srv = self.create_service(AddTwoInts, 'add_two_ints', self.add_two_ints_callback)
def add_two_ints_callback(self, request, response):
response.sum = request.a + request.b
self.get_logger().info('Incoming request\na: %d b: %d' % (request.a, request.b))
return response
def main(args=None):
rclpy.init(args=args)
minimal_service = MinimalService()
rclpy.spin(minimal_service)
rclpy.shutdown()
if __name__ == '__main__':
main()
解析代码导入消息类型,python 模块
from example_interfaces.srv import AddTwoInts
import rclpy
from rclpy.node import Node
初始化节点名字minimal_service
,创建服务add_two_ints
绑定回调 add_two_ints_callback
,并发布
def __init__(self):
super().__init__('minimal_service')
self.srv = self.create_service(AddTwoInts, 'add_two_ints', self.add_two_ints_callback)
这就是那个回调
def add_two_ints_callback(self, request, response):
response.sum = request.a + request.b
self.get_logger().info('Incoming request\na: %d b: %d' % (request.a, request.b))
return response
修改setup.py在console_scripts list里加上一行
'service = py_srvcli.service_member_function:main',
Ⅲ 写客户端节点
到 dev_ws/src/py_srvcli/py_srvcli
下新建文件client_member_function.py
demo 代码:
import sys
from example_interfaces.srv import AddTwoInts
import rclpy
from rclpy.node import Node
class MinimalClientAsync(Node):
def __init__(self):
super().__init__('minimal_client_async')
self.cli = self.create_client(AddTwoInts, 'add_two_ints')
while not self.cli.wait_for_service(timeout_sec=1.0):
self.get_logger().info('service not available, waiting again...')
self.req = AddTwoInts.Request()
def send_request(self):
self.req.a = int(sys.argv[1])
self.req.b = int(sys.argv[2])
self.future = self.cli.call_async(self.req)
def main(args=None):
rclpy.init(args=args)
minimal_client = MinimalClientAsync()
minimal_client.send_request()
while rclpy.ok():
rclpy.spin_once(minimal_client)
if minimal_client.future.done():
try:
response = minimal_client.future.result()
except Exception as e:
minimal_client.get_logger().info(
'Service call failed %r' % (e,))
else:
minimal_client.get_logger().info(
'Result of add_two_ints: for %d + %d = %d' %
(minimal_client.req.a, minimal_client.req.b, response.sum))
break
minimal_client.destroy_node()
rclpy.shutdown()
if __name__ == '__main__':
main()
代码解析import sys 为了获取输入的参数初始化节点,创建客户端
super().__init__('minimal_client_async')
self.cli = self.create_client(AddTwoInts, 'add_two_ints')
等待服务端启动
while not self.cli.wait_for_service(timeout_sec=1.0):
self.get_logger().info('service not available, waiting again...')
发送请求
minimal_client.send_request()
等待返回,返回之后打印出来,包括了几个异常退出打印
while rclpy.ok():
rclpy.spin_once(minimal_client)
if minimal_client.future.done():
try:
response = minimal_client.future.result()
except Exception as e:
minimal_client.get_logger().info(
'Service call failed %r' % (e,))
else:
minimal_client.get_logger().info(
'Result of add_two_ints: for %d + %d = %d' %
(minimal_client.req.a, minimal_client.req.b, response.sum))
break
修改setup.py在console_scripts list里加上一行
'client = py_srvcli.client_member_function:main',
最后这个样子:
from setuptools import setup
package_name = 'py_srvcli'
setup(
name=package_name,
version='0.0.0',
packages=[package_name],
data_files=[
('share/ament_index/resource_index/packages',
['resource/' + package_name]),
('share/' + package_name, ['package.xml']),
],
install_requires=['setuptools'],
zip_safe=True,
maintainer='utry',
maintainer_email='jinmenglei',
description='TODO: Package description',
license='TODO: License declaration',
tests_require=['pytest'],
entry_points={
'console_scripts': [
'service = py_srvcli.service_member_function:main',
'client = py_srvcli.client_member_function:main',
],
},
)
Ⅳ 编译和运行
养成好习惯,编译前先解决依赖,切换到dev_ws下
sudo rosdep install -i --from-path src --rosdistro eloquent -y
只编译新增的包
colcon build --packages-select py_srvcli
安装环境
. install/setup.bash
运行两个节点
ros2 run py_srvcli server
ros2 run py_srvcli client 2 3
④ 总结
您创建了两个节点来通过服务请求和响应数据。您将它们的依赖项和可执行文件添加到程序包配置文件中,可以构建和运行它们,并看到的服务/客户端系统运行起来。
这里面有个注意点就是客户端的调用方式,有两种,一个是同步call(self.req)一个是异步call_async(self.req),同步就是一直阻塞到有结果,很容易就死锁了,推荐异步
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