Difference between rospy.spin and rospy.sleep

answered 2019-09-02 17:57:03 -0600

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rospy.spin() will effectively go into an infinite loop until it receives a shutdown signal (e.g. ctrl-c). During that loop it will process any events that occur, such as data received on a topic or a timer triggering, when they occur but otherwise it will sleep. You should use spin() when your node doesn't do anything outside of its callbacks.

rospy.sleep() will do the same as rospy.spin() but only for the length of time you specify. It is used when your node has to do some kind of regular processing in addition to responding to topic events, timer events, etc. For example, a node controlling a motor will need to do some processing at regular intervals to set the motor's desired speed.

(Technically, what both are doing is sleeping your main thread and allowing other, internal threads to do their work.)

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I didn't understand the part "It is used when your node has to do some kind of regular processing in addition to responding to topic events, timer events, etc." ;( Can you please explain in codes what this would mean? If I have two functions in a node. One does image processing and the other one controls the robot. When I use rospy.sleep(20) after each function, It just waits 20 sec to run the loop again. rospy.spin() I used like this-

if __name__ == '__main__':  
    try:
        talker()
        main(sys.argv)
        rospy.spin()
    except rospy.ROSInterruptException:
        pass

Here main() has a call to another function in it's code. So my question is does rospy.spin() run this try: block of code again and again?

Shivam ( 2021-10-04 08:19:02 -0600 )edit

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