| Note: This tutorial assumes that you have completed the previous tutorials: writing a simple action server using the execute callback method. |
 Please ask about problems and questions regarding this tutorial on answers.ros.org. Don't forget to include in your question the link to this page, the versions of your OS & ROS, and also add appropriate tags. |
Writing a Simple Action Client
Description: This tutorial covers using the simple_action_client library to create a Fibonacci action client. This example program creates an action client and sends a goal to the action server.Tutorial Level: BEGINNER
Contents
The Code
First, create actionlib_tutorials/src/fibonacci_client.cpp in your favorite editor, and place the following inside it:
1 #include <ros/ros.h>
2 #include <actionlib/client/simple_action_client.h>
3 #include <actionlib/client/terminal_state.h>
4 #include <actionlib_tutorials/FibonacciAction.h>
5
6 int main (int argc, char **argv)
7 {
8 ros::init(argc, argv, "test_fibonacci");
9
10 // create the action client
11 // true causes the client to spin its own thread
12 actionlib::SimpleActionClient<actionlib_tutorials::FibonacciAction> ac("fibonacci", true);
13
14 ROS_INFO("Waiting for action server to start.");
15 // wait for the action server to start
16 ac.waitForServer(); //will wait for infinite time
17
18 ROS_INFO("Action server started, sending goal.");
19 // send a goal to the action
20 actionlib_tutorials::FibonacciGoal goal;
21 goal.order = 20;
22 ac.sendGoal(goal);
23
24 //wait for the action to return
25 bool finished_before_timeout = ac.waitForResult(ros::Duration(30.0));
26
27 if (finished_before_timeout)
28 {
29 actionlib::SimpleClientGoalState state = ac.getState();
30 ROS_INFO("Action finished: %s",state.toString().c_str());
31 }
32 else
33 {
34 ROS_INFO("Action did not finish before the time out.");
35 ac.cancelGoal();
36 }
37
38 //exit
39 return 0;
40 }
(Original can be found on the repository of the tutorial package)
The Code Explained
Now, let's break down the code piece by piece.
actionlib/client/simple_action_client.h is the action library used from implementing simple action clients.
actionlib/client/terminal_state.h defines the possible goal states.
This includes action message generated from the Fibonacci.action file shown above. This is a header generated automatically from the FibonacciAction.msg file. For more information on message definitions, see the msg page.
The action client is templated on the action definition, specifying what message types to communicate to the action server with. The action client constructor also takes two arguments, the server name to connect to and a boolean option to automatically spin a thread. If you prefer not to use threads (and you want actionlib to do the 'thread magic' behind the scenes), this is a good option for you. Here the action client is constructed with the server name and the auto spin option set to true.
Since the action server may not be up and running, the action client will wait for the action server to start before continuing.
Here a goal message is created, the goal value is set and sent to the action server.
The action client now waits for the goal to finish before continuing. The timeout on the wait is set to 30 seconds, this means after 30 seconds the function will return with false if the goal has not finished.
If the goal finished before the time out the goal status is reported, else the user is notified that the goal did not finish in the allotted time.
Compiling
Add the following lines to your CMakeLists.txt file:
add_executable(fibonacci_client src/fibonacci_client.cpp)
target_link_libraries(
fibonacci_client
${catkin_LIBRARIES}
)
add_dependencies(
fibonacci_client
${actionlib_tutorials_EXPORTED_TARGETS}
)Then build:
cd %TOPDIR_YOUR_CATKIN_WORKSPACE% catkin_make source devel/setup.bash
rosbuild_add_executable(fibonacci_client src/fibonacci_client.cpp) rosbuild_link_boost(fibonacci_client thread)
Running the Action client
After you have successfully built the executable, start a new terminal and run the client:
$ rosrun actionlib_tutorials fibonacci_client
You will see something similar to:
[ INFO] 1250806286.804217000: Started node [/test_fibonacci], pid [9414], bound on [aqy], xmlrpc port [35466], tcpros port [55866], logging to [~/ros/ros/log/test_fibonacci_9414.log], using [real] time [ INFO] 1250806287.828279000: Waiting for action server to start.
To check that your client is running properly, list ROS topics being published:
$ rostopic list -v
You will see something similar to:
Published topics: * /fibonacci/goal [actionlib_tutorials/FibonacciActionGoal] 1 publisher * /fibonacci/cancel [actionlib_msgs/GoalID] 1 publisher * /rosout [rosgraph_msgs/Log] 1 publisher * /rosout_agg [rosgraph_msgs/Log] 1 publisher Subscribed topics: * /fibonacci/feedback [actionlib_tutorials/FibonacciActionFeedback] 1 subscriber * /rosout [rosgraph_msgs/Log] 1 subscriber * /fibonacci/status [actionlib_msgs/GoalStatusArray] 1 subscriber * /fibonacci/result [actionlib_tutorials/FibonacciActionResult] 1 subscriber
Alternatively you can look at the nodes:
$ rxgraph
Or, starting with Groovy:
$ rqt_graph
This shows that your client is subscribing to the feedback, status, and result channels as expected and publishing to the goal and cancel channels as expected. The client is up and running properly.
Connecting the Server and Client
For the next step in using your action, you need to Ctrl-C the action client and run the action server and client.
