waitfor

Pause code execution to achieve desired execution rate

Since R2022b

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.

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

Examples

Run Loop at Fixed Rate Using ros2rate

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: 0.003713
Iteration: 2 - Time Elapsed: 0.503948
Iteration: 3 - Time Elapsed: 1.002066
Iteration: 4 - Time Elapsed: 1.501915
Iteration: 5 - Time Elapsed: 2.003118
Iteration: 6 - Time Elapsed: 2.509287
Iteration: 7 - Time Elapsed: 3.000224
Iteration: 8 - Time Elapsed: 3.500617
Iteration: 9 - Time Elapsed: 4.000167
Iteration: 10 - Time Elapsed: 4.500382

Input Arguments

rate — ros2rate object

handle

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

numMisses — Number of missed task executions

scalar

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