waitfor

Pause code execution to achieve desired execution rate

Since R2022b

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    Syntax

    waitfor(rate)
    numMisses = waitfor(rate)

    Description

    waitfor(rate) pauses execution of the ROS 2 loop execution object rate until the code reaches the desired execution rate. The function accounts for the time spent executing code between waitfor calls.

    example

    numMisses = waitfor(rate) returns the number of iterations missed while executing code between calls.

    Examples

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    Open Live Script

    Create a ROS 2 node.

    node = ros2node("/myNode");

    Create a publisher to publish a standard integer message.

    pub = ros2publisher(node,"/my_int","std_msgs/Int64");

    Create a ros2rate object that runs at 2 Hz.

    r = ros2rate(node,2);

    Start loop that prints the current iteration and time elapsed. Use waitfor to pause the loop until the next time interval. Reset r prior to the loop execution. Notice that each iteration executes at a 1-second interval.

    reset(r)
for i = 1:10
	time = r.TotalElapsedTime;
	fprintf('Iteration: %d - Time Elapsed: %f\n',i,time)
	waitfor(r);
end
    Iteration: 1 - Time Elapsed: 0.006865
Iteration: 2 - Time Elapsed: 0.506501
Iteration: 3 - Time Elapsed: 1.003673
Iteration: 4 - Time Elapsed: 1.502877
Iteration: 5 - Time Elapsed: 2.005498
Iteration: 6 - Time Elapsed: 2.519913
Iteration: 7 - Time Elapsed: 3.000348
Iteration: 8 - Time Elapsed: 3.500132
Iteration: 9 - Time Elapsed: 4.000324
Iteration: 10 - Time Elapsed: 4.500440

    Input Arguments

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    ros2rate object, specified as a handle. This object contains the information for the desired rate and other information about the execution. See ros2rate for more information.

    Output Arguments

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    Number of missed task executions, returned as a scalar. waitfor returns the number of desired time steps missed based on the LastPeriod and DesiredRate properties of the ros2rate object rate. For example, if the desired rate is 1 Hz and the last period was 3.2 seconds, numMisses is 3.

    Version History

    Introduced in R2022b

    See Also