| Note: This tutorial assumes that you have completed the previous tutorials: writing a simple action server using the execute callback method. |
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
Next Tutorial: Run the action server and client
Contents
The Code
First, create learning_actionlib/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 <learning_actionlib/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 it's own thread
12 actionlib::SimpleActionClient<learning_actionlib::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 learning_actionlib::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 ROS_INFO("Action did not finish before the time out.");
34
35 //exit
36 return 0;
37 }
The Code Explained
Now, let's break down the code piece by piece.
1 #include <ros/ros.h>
2 #include <actionlib/client/simple_action_client.h>
3 #include <actionlib/client/terminal_state.h>
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.
4 #include <learning_actionlib/FibonacciAction.h>
This includes action message generated from the Fibonacci.action file show above. This is a header generated automatically from the FibonacciAction.msg file. For more information on message definitions, see the msg page.
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 it's own thread
12 actionlib::SimpleActionClient<learning_actionlib::FibonacciAction> ac("fibonacci", true);
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.
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
Since the action server may not be up and running, the action client will wait for the action server to start before continuing.
17 ROS_INFO("Action server started, sending goal.");
18 // send a goal to the action
19 learning_actionlib::FibonacciGoal goal;
20 goal.order = 20;
21 ac.sendGoal(goal);
Here a goal message is created, the goal value is set and sent to the action server.
24 //wait for the action to return
25 bool finished_before_timeout = ac.waitForResult(ros::Duration(30.0));
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.
26 if (finished_before_timeout)
27 {
28 actionlib::SimpleClientGoalState state = ac.getState();
29 ROS_INFO("Action finished: %s",state.toString().c_str());
30 }
31 else
32 ROS_INFO("Action did not finish before the time out.");
33
34 //exit
35 return 0;
36 }
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 and Running the Client
Add the following line to your CMakeLists.txt file:
rosbuild_add_executable(fibonacci_client src/fibonacci_client.cpp)
After you have made the executable, start a roscore in a new terminal
$ roscore
And then run the client:
$ rosrun learning_actionlib 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/GoalID] 1 publisher * /rosout [roslib/Log] 1 publisher * /rosout_agg [roslib/Log] 1 publisher Subscribed topics: * /time [unknown type] 2 subscribers * /rosout [roslib/Log] 1 subscriber * /fibonacci/feedback [unknown type] 1 subscriber * /fibonacci/status [unknown type] 1 subscriber * /fibonacci/result [unknown type] 1 subscriber
Alternatively you can look at the nodes:
$ rxgraph -t
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.