waitForServer
Syntax
Description
waitForServer(
waits until the action
server is started up and available to send goals. The client
)IsServerConnected
property of the ros2actionClient
object shows the status of the server
connection. Press Ctrl+C to cancel the wait.
waitForServer(
specifies a timeout period in seconds using the name-value argument
client
,Timeout=timeoutperiod)Timeout=timeoutperiod
. If the action server does not start up in the
timeout period, this function displays an error and lets MATLAB® continue running the current program. The default value of
inf
prevents MATLAB from running the current program until the action client receives a
response.
[
returns a status
,statustext
] = waitForServer(___)status
indicating whether the action server is available, and
a statustext
that captures additional information about the
status
, using any of the arguments from the previous syntaxes. If the
server is not available within the Timeout
, status
will be false
, and this function will not display an error.
Examples
Set Up ROS 2 Action Client and Execute an Action
This example shows how to create a ROS 2 action client and execute the action. Action types must be set up beforehand with an action server running. This example uses the /fibonacci
action. Follow these steps to set up the action server:
Create a ROS 2 package with the action definition. For instructions on setting up a /
fibonacci
action, see Creating an Action.Create a ROS 2 package with the action server implementation. For more information on setting up the
/fibonacci
action server, see Writing an Action Server.Use the
ros2genmsg
function for the ROS 2 package with action definition from Step 1, and generate action messages in MATLAB®.
To run the /fibonacci
action server, use this command on the ROS 2 system:
ros2 run action_tutorials_cpp fibonacci_action_server
Set Up ROS 2 Action Client
List the actions available on the network. The /fibonacci
action must be on the list.
ros2 action list
/fibonacci
Get the action type for the /fibonacci
action.
ros2 action type /fibonacci
action_tutorials_interfaces/Fibonacci
Create a ROS 2 node.
node = ros2node("/node_1");
Create an action client by specifying the node, action name, and action type. Set the quality of service (QoS) parameters.
[client,goalMsg] = ros2actionclient(node,"fibonacci",... "action_tutorials_interfaces/Fibonacci", ... CancelServiceQoS=struct(Depth=200,History="keeplast"), ... FeedbackTopicQoS=struct(Depth=200,History="keepall"));
Wait for the action client to connect to the server.
status = waitForServer(client)
status = logical
1
The /fibonacci
action will calculate the Fibonacci sequence for a given order specified in the goal message. The goal message was returned when creating the action client and can be modified to send goals to the ROS action server. Set the order to an int32
value of 8. If the input requires a 1-D array, set it as a column vector.
goalMsg.order = int32(8);
Send Goal and Execute Action
Before sending the goal, define the callback options framework for the goal execution process. In this example, you specify a callback function to execute when the server returns a feedback response and the final result using the name-value arguments.
callbackOpts = ros2ActionSendGoalOptions(FeedbackFcn=@helperFeedbackCallback,ResultFcn=@helperResultCallback);
Send the goal to the action server using the sendGoal
function. Specify the callback options. During goal execution, you see outputs from the feedback and result callbacks displayed on the MATLAB® command window.
goalHandle = sendGoal(client,goalMsg,callbackOpts);
Goal with GoalUUID 3d10ab880f960666fde5666f45f621a accepted by server, waiting for result! Partial sequence feedback for goal 3d10ab880f960666fde5666f45f621a is 0 1 1 Partial sequence feedback for goal 3d10ab880f960666fde5666f45f621a is 0 1 1 2 Partial sequence feedback for goal 3d10ab880f960666fde5666f45f621a is 0 1 1 2 3 Partial sequence feedback for goal 3d10ab880f960666fde5666f45f621a is 0 1 1 2 3 5 Partial sequence feedback for goal 3d10ab880f960666fde5666f45f621a is 0 1 1 2 3 5 8 Partial sequence feedback for goal 3d10ab880f960666fde5666f45f621a is 0 1 1 2 3 5 8 13 Partial sequence feedback for goal 3d10ab880f960666fde5666f45f621a is 0 1 1 2 3 5 8 13 21 Full sequence result for goal 3d10ab880f960666fde5666f45f621a is 0 1 1 2 3 5 8 13 21
Get the status of goal execution.
exStatus = getStatus(client,goalHandle)
exStatus = int8
2
Get the result using the action client and goal handle inputs. Display the result. The getResult
function returns the sequence as a column vector.
resultMsg = getResult(client,goalHandle); rosShowDetails(resultMsg)
ans = ' MessageType : action_tutorials_interfaces/FibonacciResult sequence : [0, 1, 1, 2, 3, 5, 8, 13, 21]'
Alternatively, you can only use the goal handle as input to get the result.
resultMsg = getResult(goalHandle); rosShowDetails(resultMsg)
ans = ' MessageType : action_tutorials_interfaces/FibonacciResult sequence : [0, 1, 1, 2, 3, 5, 8, 13, 21]'
Helper Functions
helperFeedbackCallback
defines the callback function to execute when the client receives a feedback response from the action server.
function helperFeedbackCallback(goalHandle,feedbackMsg) seq = feedbackMsg.partial_sequence; disp(['Partial sequence feedback for goal ',goalHandle.GoalUUID,' is ',num2str(seq')]) end
helperResultCallback
defines the callback function to execute when the client receives the result message from the action server.
function helperResultCallback(goalHandle,wrappedResultMsg) seq = wrappedResultMsg.result.sequence; disp(['Full sequence result for goal ',goalHandle.GoalUUID,' is ',num2str(seq')]) end
Send and Cancel ROS 2 Action Goals
This example shows how to send and cancel ROS 2 action goals. Action types must be set up beforehand with an action server running. This example uses the /fibonacci
action. Follow these steps to set up the action server:
Create a ROS 2 package with the action definition. For instructions on setting up a /
fibonacci
action, see Creating an Action.Create a ROS 2 package with the action server implementation. For more information on setting up the
/fibonacci
action server, see Writing an Action Server.Use the
ros2genmsg
function for the ROS 2 package with action definition from Step 1, and generate action messages in MATLAB®.
To run the /fibonacci
action server, use this command on the ROS 2 system:
ros2 run action_tutorials_cpp fibonacci_action_server
Set Up ROS 2 Action Client
Create a ROS 2 node.
node = ros2node("/node_1");
Create an action client for /fibonacci
action by specifying the node, action name, and action type. Set the quality of service (QoS) parameters.Wait for the action client to connect to the server.
[client,goalMsg] = ros2actionclient(node,"fibonacci",... "action_tutorials_interfaces/Fibonacci", ... CancelServiceQoS=struct(Depth=200,History="keeplast"), ... FeedbackTopicQoS=struct(Depth=200,History="keepall")); status = waitForServer(client)
status = logical
1
Before sending the goal, define the callback options framework for the goal execution process. In this example, you specify a callback function to execute when the server returns a feedback response.
callbackOpts = ros2ActionSendGoalOptions(FeedbackFcn=@helperFeedbackCallback);
Send and Cancel Goals
The /fibonacci
action will calculate the /fibonacci
sequence for a given order specified in the goal message. The goal message was returned when creating the action client and can be modified to send goals to the ROS action server. Set the order to an int32
value of 8.
goalMsg.order = int32(8);
Create a new goal message and set the order to an int32
value of 10.
goalMsg2 = ros2message(client); goalMsg2.order = int32(10);
Send both the goals to the action server using the sendGoal
function. Specify the same callback options for both goals.
goalHandle = sendGoal(client,goalMsg,callbackOpts); goalHandle2 = sendGoal(client,goalMsg2,callbackOpts);
Goal with GoalUUID ca8dbca2b8608a6f2add01b298f6930 accepted by server, waiting for result! Partial sequence feedback for goal ca8dbca2b8608a6f2add01b298f6930 is 0 1 1 Goal with GoalUUID f493913f4acd2224f31145ae74bbc35 accepted by server, waiting for result! Partial sequence feedback for goal f493913f4acd2224f31145ae74bbc35 is 0 1 1
Cancel the specific goal associated with the sequence order 8
. Use the goal handle object associated with that goal as input to the cancelGoal
function, and specify the cancel callback to execute once the client receives the cancel response. This function returns immediately without waiting for the cancel response to arrive.
cancelGoal(client,goalHandle,CancelFcn=@helperCancelGoalCallback)
Goal ca8dbca2b8608a6f2add01b298f6930 is cancelled with return code 0
You can wait until the cancel response arrives from the server by using the cancelGoalAndWait
function. Cancel the goal associated with the sequence order of 10 and wait until the client receives the cancel response.
cancelResponse = cancelGoalAndWait(client,goalHandle2)
cancelResponse = struct with fields:
MessageType: 'action_msgs/CancelGoalResponse'
ERROR_NONE: 0
ERROR_REJECTED: 1
ERROR_UNKNOWN_GOAL_ID: 2
ERROR_GOAL_TERMINATED: 3
return_code: 0
goals_canceling: [1×1 struct]
Cancel Goals Before Timestamp
Send the goal message with sequence order 10
. Note the timestamp in a ROS 2 message by using the ros2time
function.
goalHandle = sendGoal(client,goalMsg2,callbackOpts);
timeStampMsg = ros2time(node,"now");
Goal with GoalUUID d8268c566b234e8784f0f1a8ec12b2 accepted by server, waiting for result! Partial sequence feedback for goal d8268c566b234e8784f0f1a8ec12b2 is 0 1 1
Then, send a second goal message with sequence order 8
. Note the timestamp.
goalHandle2 = sendGoal(client,goalMsg,callbackOpts);
timeStampMsg2 = ros2time(node,"now");
Goal with GoalUUID 9585bff2ba44bf60daa630a952b458be accepted by server, waiting for result! Partial sequence feedback for goal 9585bff2ba44bf60daa630a952b458be is 0 1 1
Cancel the goal sent before the first time stamp using cancelGoalsBefore
function.
cancelGoalsBefore(client,timeStampMsg,CancelFcn=@helperCancelGoalsCallback)
Goals cancelled with return code 0
Use the cancelGoalsBeforeAndWait
function to cancel the goal sent before second time stamp and wait for the cancel response.
cancelResponse = cancelGoalsBeforeAndWait(client,timeStampMsg2)
cancelResponse = struct with fields:
MessageType: 'action_msgs/CancelGoalResponse'
ERROR_NONE: 0
ERROR_REJECTED: 1
ERROR_UNKNOWN_GOAL_ID: 2
ERROR_GOAL_TERMINATED: 3
return_code: 0
goals_canceling: [1×1 struct]
Cancel All Goals
Cancel all the active goals that the client sent.
goalHandle = sendGoal(client,goalMsg,callbackOpts); cancelAllGoals(client,CancelFcn=@helperCancelGoalsCallback);
Goals cancelled with return code 0
Cancel all the active goals that the client sent and wait for cancel response.
goalHandle2 = sendGoal(client,goalMsg2,callbackOpts); cancelResponse = cancelAllGoalsAndWait(client)
cancelResponse = struct with fields:
MessageType: 'action_msgs/CancelGoalResponse'
ERROR_NONE: 0
ERROR_REJECTED: 1
ERROR_UNKNOWN_GOAL_ID: 2
ERROR_GOAL_TERMINATED: 3
return_code: 0
goals_canceling: [1×1 struct]
Helper Functions
helperFeedbackCallback
defines the callback function to execute when the client receives a feedback response from the action server.
function helperFeedbackCallback(goalHandle,feedbackMsg) seq = feedbackMsg.partial_sequence; disp(['Partial sequence feedback for goal ',goalHandle.GoalUUID,' is ',num2str(seq')]) end
helperCancelGoalCallback
defines the callback function to execute when the client receives a cancel response after canceling a specific goal.
function helperCancelGoalCallback(goalHandle,cancelMsg) code = cancelMsg.return_code; disp(['Goal ',goalHandle.GoalUUID,' is cancelled with return code ',num2str(code)]) end
helperCancelGoalsCallback
defines the callback function to execute when the client receives a cancel response after canceling a set of goals.
function helperCancelGoalsCallback(cancelMsg) code = cancelMsg.return_code; disp(['Goals cancelled with return code ',num2str(code)]) end
Input Arguments
client
— ROS 2 action client
ros2actionclient
object handle
ROS 2 action client, specified as a ros2actionclient
object
handle.
Output Arguments
status
— Status of the action server start up
logical
scalar
Status of the action server start up, returned as a logical
scalar. If the server is not available within the timeout period,
status
will be false
.
Note
Use the status
output argument when you use waitForServer for code
generation. This will avoid runtime errors and outputs the status instead, which can be
reacted to in the calling code.
statustext
— Status text associated with the action server status
character vector
Status text associated with the action server status, returned as one of the following:
'success'
— The server is available.'input'
— The input to the function is invalid.'timeout'
— The server did not become available before the timeout period expired.
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.
Version History
Introduced in R2023a
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