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how to monitor topic, when a certain topic not exist?

asked 2016-10-28 07:59:15 -0500

jxl gravatar image

Hello,

I want to do a such thing : To monitor a topic . When everything is OK, a certain topic is always published by node A at a rate. when something wrong ,the node A is died,and the topic does not exist .At this time ,how can i know this topic exist or not ?

Does ROS has such API to monitor a topic ,when it does not exist ,notify me and i can use this signal to do something i want.

Any suggestions will be appreciated ,thank you very much !!!

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answered 2016-10-31 17:43:43 -0500

NEngelhard gravatar image

The subscriber knows to how many publishers it is connected to: getNumPublishers Or you use rospy to directly get a list of published topics: get_published_topics.

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Wow! I learn something new every day! Sorry about giving a completely wrong answer!

Kurt Leucht gravatar image Kurt Leucht  ( 2016-11-01 08:56:30 -0500 )edit

Thanks a lot ~~

jxl gravatar image jxl  ( 2016-11-09 02:34:55 -0500 )edit
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answered 2016-10-31 12:43:27 -0500

ROS is designed, as far as I know, to not care whether Topics exist or not. ROS will let Subscribers sit all day waiting for data on non-existant Topics.

One solution is to set up a watchdog style timer that looks for data on the topic and lets you know if a certain period of time occurs without any new data coming in.

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The messages are sent via TCP so that there is an open connection to every publisher. The subscriber therefore has to know who is currently publishing.

NEngelhard gravatar image NEngelhard  ( 2016-11-01 13:10:11 -0500 )edit

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Asked: 2016-10-28 07:59:15 -0500

Seen: 666 times

Last updated: Oct 31 '16