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Can subscriber know if publisher is latched=true?

asked 2012-11-21 11:42:42 -0500

jihoonl gravatar image

It may be useful

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I'd argue that only publishers should be latched on topics which use case is indifferent of knowing they are latched. Could you think of some example?

felix k gravatar image felix k  ( 2013-09-29 21:28:03 -0500 )edit

One usecase is rosbridge node which is a subscriber of topic message but also publisher to the web clients. The problem was that one rosbridge client which came late couldn't receive the topic message if two rosbridge clients attempt to subscribe a latch topic.

jihoonl gravatar image jihoonl  ( 2013-12-08 20:47:03 -0500 )edit

um.. maybe this issue describes better https://github.com/RobotWebTools/rosbridge_suite/issues/1

jihoonl gravatar image jihoonl  ( 2013-12-08 20:51:30 -0500 )edit

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answered 2013-09-29 21:25:30 -0500

felix k gravatar image

I'd think comparing the time of ones own (successfull) subscription to the timestamp in the message could serve as a workaround, if the mechanical details are checked. Like that the subscriber initialization probably returns before the subscription at the rosmaster is completed.

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This assumes that a message's time stamp is (near) the current time, when it was sent, which isn't necessarily true.

dornhege gravatar image dornhege  ( 2013-09-29 22:55:21 -0500 )edit
jihoonl gravatar image jihoonl  ( 2013-12-08 20:53:37 -0500 )edit

This question was to support rosbridge. and we got it workaround with this pull request. Thanks all https://github.com/RobotWebTools/rosbridge_suite/pull/58

jihoonl gravatar image jihoonl  ( 2013-12-08 20:54:49 -0500 )edit
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answered 2013-09-29 20:20:08 -0500

tfoote gravatar image

I do not think that this is introspectable, it is just a behavior.

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Asked: 2012-11-21 11:42:42 -0500

Seen: 402 times

Last updated: Sep 29 '13