From rospy Time wiki entry,
rospy.Rate(hz)
rospy provides a rospy.Rate
convenience class which makes a best
effort at maintaining a particular
rate for a loop. For example:
r = rospy.Rate(10) # 10hz
while not rospy.is_shutdown():
pub.publish("hello")
r.sleep()
In the above example, the Rate
instance will attempt to keep the loop
at 10hz by accounting for the time
used by any operations during the
loop. Rate.sleep() can throw a
rospy.ROSInterruptException if the
sleep is interrupted by shutdown.
Basically, it allows your loops to run at (nearly) the exact rate (in Hz) that you specify. It's a pretty standard way of looping with ROS. Check out the source code that's linked to in the documentation that you were looking at:
87 - def sleep(self):
88 """
89 Attempt sleep at the specified rate. sleep() takes into
90 account the time elapsed since the last successful
91 sleep().
92
93 @raise ROSInterruptException: if ROS shutdown occurs before
94 sleep completes
95 @raise ROSTimeMovedBackwardsException: if ROS time is set
96 backwards
97 """
98 curr_time = rospy.rostime.get_rostime()
99 sleep(self._remaining(curr_time))
100 self.last_time = self.last_time + self.sleep_dur
101
102 # detect time jumping forwards, as well as loops that are
103 # inherently too slow
104 if curr_time - self.last_time > self.sleep_dur * 2:
105 self.last_time = curr_time
Go through the rospy tutorials if you haven't already. From the writing a publisher and subscriber tutorial:
rate = rospy.Rate(10) # 10hz
This line creates a Rate object rate. With the help of its method
sleep(), it offers a convenient way
for looping at the desired rate. With
its argument of 10, we should expect
to go through the loop 10 times per
second (as long as our processing time
does not exceed 1/10th of a second!)
Originally posted by jayess with karma: 6155 on 2017-06-26
This answer was ACCEPTED on the original site
Post score: 12
Original comments
Comment by img5d on 2019-07-24:
good answer.
Comment by lxg on 2020-08-06:
thanks for the answer. but what happens if the process timing exceeds 1/10th of a second?
Comment by jayess on 2020-08-06:
That really shouldn't change anything as long as your computer can handle it
Comment by lxg on 2020-08-07:
Thanks jayes. so is it safe to conclude that all the code within the while loop above will execute 10 times a second as long as the computer can handle it? regardless of the code within the while loop?
Comment by jayess on 2020-08-07:
I wouldn't want to make any sweeping generalizations, but I'd say generally yes. If you examine the code above, basically what's happening is that a call to r.sleep() sleeps for the amount of time needed to keep the loop running at the given rate as best as it can.
Comment by lxg on 2020-08-07:
alright, thank you. Does r.sleep() trying to maintain the given rate have anything to do with python scripts running even after Ctr + C is pressed. I mean ROS definitely stops but the script keeps executing especially if there are loops within the while loop. especially data read from a buffer. Could it be related or is it an entirely different issue?
Comment by jayess on 2020-08-08:
I'd say probably not, but if this is an issue that you're having then you should post a question about it
Comment by lxg on 2020-08-09:
thanks. i did. and it got answered.