actionlib学习
ROS中的服务service是一问一答的形式,你来查询了,我就返给你要的信息。
action也有服务的概念,但是它不一样的地方是:不是一问一答,而多了一个反馈,它会不断反馈项目进度。
如navigation下的move_base package,你设定了目标点,反馈信息可能是机器人在规划路径上的即时位姿,
直到机器人到达目标点,返回SUCCEEDED消息。
上面所述的 ActionClient 和 ActionServer 通过 ROS Action Protocol (ROS Action 协议,建立在ROS messages的基础上)来通信。
Client&Server 为用户提供了简单的API,通过函数的调用和回调,用来在client端request一个目标,或者,在server端来执行达成一个目标。
下图说明这个机制如何运行:
Action Specification: Goal, Feedback, & Result
Goal:
为了用actions机制完成一个任务,我们引入了the notion of a goal, 这个goal可以被ActionClient发送到ActionServer. 比如在move base
这个案例中,它的类型是PoseStamped,包含了机器人应该到达的哪里的信息。在激光扫描云台控制案例中,the goal会包含扫描的参数
(min angle, max angle, speed 等)
Feedback
Feedback是server用来告诉ActionClient goal执行过程中的各种情况。在moving_base案例中,它是机器人现在的位姿;
在controlling the tilting laser scanner案例中, this might be the time left until the scan completes(扫描剩余时间).
Result
执行结果,比如在move_base中的结果和机器人pose;在云台激光扫描中的一个请求的点云数据。等
下面写一个actionlib的c++例程
catkin_create_pkg actionlib_tutorials roscpp rospy actionlib actionlib_msgs message_generation
在包中添加action文件夹在里面新建一个 Fibonacci.action文件
#goal definition int32 order --- #result definition int32[] sequence --- #feedback definition int32[] sequence
修改package.xml添加
<run_depend>message_generation</run_depend>
修改 CMakeLists.txt删除添加;编译cpp文件根据自己的添加
add_action_files(
DIRECTORY action
FILES Fibonacci.action
) generate_messages(DEPENDENCIES actionlib_msgs ) CATKIN_DEPENDS actionlib actionlib_msgs message_generation roscpp rospy
简单的client.cpp
#include <ros/ros.h> #include <actionlib/client/simple_action_client.h> #include <actionlib_tutorials/FibonacciAction.h> using namespace actionlib_tutorials; typedef actionlib::SimpleActionClient<FibonacciAction> Client; int main (int argc, char **argv) { ros::init(argc, argv, "test_fibonacci_callback"); // Create the action client Client ac("fibonacci", true); ROS_INFO("Waiting for action server to start."); ac.waitForServer(); ROS_INFO("Action server started, sending goal."); // Send Goal FibonacciGoal goal; goal.order = 10; ac.sendGoal(goal); bool finish_before_timeout=ac.waitForResult(ros::Duration(15)); if(finish_before_timeout) { actionlib::SimpleClientGoalState state = ac.getState(); ROS_INFO("action finish : %s",state.getState().toString().c_str()); }else { ROS_INFO("TIMEOUT"); } ros::spin(); return 0; }
带回调显示的clientprocess.cpp
#include <ros/ros.h> #include <actionlib/client/simple_action_client.h> #include <actionlib_tutorials/FibonacciAction.h> using namespace actionlib_tutorials; typedef actionlib::SimpleActionClient<FibonacciAction> Client; // Called once when the goal completes void doneCb(const actionlib::SimpleClientGoalState& state, const FibonacciResultConstPtr& result) { ROS_INFO("Finished in state [%s]", state.toString().c_str()); ROS_INFO("Answer: %i", result->sequence.back()); ros::shutdown(); } // Called once when the goal becomes active void activeCb() { ROS_INFO("Goal just went active"); } // Called every time feedback is received for the goal void feedbackCb(const FibonacciFeedbackConstPtr& feedback) { ROS_INFO("Got Feedback of length %lu", feedback->sequence.size()); } int main (int argc, char **argv) { ros::init(argc, argv, "test_fibonacci_callback"); // Create the action client Client ac("fibonacci", true); ROS_INFO("Waiting for action server to start."); ac.waitForServer(); ROS_INFO("Action server started, sending goal."); // Send Goal FibonacciGoal goal; goal.order = 20; ac.sendGoal(goal, &doneCb, &activeCb, &feedbackCb); ros::spin(); return 0; }
server.cpp
#include <ros/ros.h> #include <actionlib/server/simple_action_server.h> #include <actionlib_tutorials/FibonacciAction.h> typedef actionlib::SimpleActionServer<actionlib_tutorials::FibonacciAction> Server; class FibonacciAction { protected: ros::NodeHandle nh_; Server as_; // NodeHandle instance must be created before this line. Otherwise strange error occurs. std::string action_name_; // create messages that are used to published feedback/result actionlib_tutorials::FibonacciFeedback feedback_; actionlib_tutorials::FibonacciResult result_; public: FibonacciAction(std::string name) : as_(nh_, name, boost::bind(&FibonacciAction::executeCB, this, _1), false), action_name_(name) { as_.start(); } ~FibonacciAction(void) { } void executeCB(const actionlib_tutorials::FibonacciGoalConstPtr &goal) { // helper variables ros::Rate r(1); bool success = true; // push_back the seeds for the fibonacci sequence feedback_.sequence.clear(); feedback_.sequence.push_back(0); feedback_.sequence.push_back(1); // publish info to the console for the user ROS_INFO("%s: Executing, creating fibonacci sequence of order %i with seeds %i, %i", action_name_.c_str(), goal->order, feedback_.sequence[0], feedback_.sequence[1]); // start executing the action for(int i=1; i<=goal->order; i++) { // check that preempt has not been requested by the client if (as_.isPreemptRequested() || !ros::ok()) { ROS_INFO("%s: Preempted", action_name_.c_str()); // set the action state to preempted as_.setPreempted(); success = false; break; } feedback_.sequence.push_back(feedback_.sequence[i] + feedback_.sequence[i-1]); // publish the feedback as_.publishFeedback(feedback_); // this sleep is not necessary, the sequence is computed at 1 Hz for demonstration purposes r.sleep(); } if(success) { result_.sequence = feedback_.sequence; ROS_INFO("%s: Succeeded", action_name_.c_str()); // set the action state to succeeded as_.setSucceeded(result_); } } }; int main(int argc, char** argv) { ros::init(argc, argv, "fibonacci"); FibonacciAction fibonacci("fibonacci"); ros::spin(); return 0; }
编译后运行
rosrun actionlib_tutorials client
rosrun actionlib_tutorials sever
在设置时间内服务完成则状态输出完成,否则反馈失败,这种等待模式效率太低
rosrun actionlib_tutorials clientprocess rosrun actionlib_tutorials sever
将动作完成过程实时的将状态反馈回来,直到动作完成或失败