Question

The documentation for topic_tools/mux says:

IMPORTANT: To avoid conflicting with other instances of mux, you should always remap the mux's node name to something descriptive, using the mux:=foo syntax on the command line.

And indeed if I run

$ rosrun topic_tools mux output input1 input2 mux:=foobar & 
$ rosservice list

I can see through the service list that the node's services has been remapped to /foobar/add and so on.

However if I put the equivalent entry in my launch.xml:

<node name="mux" pkg="topic_tools" type="mux" args="output input1 input2">
    <remap from="mux" to="foobar" />
</node>

then the remapping does not work; the service uses the default names of /mux/add, etc.

The process list entries seem similar:

# roslaunch, not working
/opt/ros/noetic/lib/topic_tools/mux output input1 input2 mux:=foobar __name:=mux __log:=/root/.ros/log/1edcbb1e-ea9d-11ec-a797-0242ac110002/mux-7.log

# rosrun, working
/opt/ros/noetic/lib/topic_tools/mux output input1 input2 mux:=foobar

The behavior is baffling. When __name:=mux is provided, the topic remapping does not work. But if I omit __name:=mux or provide ANY name other than mux the remapping succeeds.

I could possibly understand if the remapping mux:=foobar caused __name:=mux to become __name:=foobar but it doesn't make sense for __name:=mux to cause mux:=foobar to be ignored.

Asked by rgov on 2022-06-12 17:25:44 UTC

Answer 1

if I run
$ rosrun topic_tools mux output input1 input2 mux:=foobar & 
$ rosservice list
I can see through the service list that the node's services has been remapped to /foobar/add and so on.

However if I put the equivalent entry in my launch.xml:
<node name="mux" pkg="topic_tools" type="mux" args="output input1 input2">
    <remap from="mux" to="foobar" />
</node>

Shouldn't you be changing the name attribute of your node instead?

That's what the documentation of topic_tools suggests: using a different node name.

The behavior is baffling.

I don't believe it is. This command line:

/opt/ros/noetic/lib/topic_tools/mux output input1 input2 mux:=foobar __name:=mux __log:=/root/.ros/log/1edcbb1e-ea9d-11ec-a797-0242ac110002/mux-7.log

essentially just starts mux, asks it to remap a resource called mux to be remapped to foobar, and then sets the node name to mux.

It's likely the __name argument takes precedence, and that rosrun without __name will afterwards apply the remap, changing all private services of mux to use the name(space) foobar.

But then again, changing names of nodes in .launch files should be done by setting the name attribute of node elements. Not using remap.

Asked by gvdhoorn on 2022-06-13 02:48:56 UTC

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The documentation for mux says to use mux:=asdf. I just created a launch file with <node name="asdf" pkg="topic_tools" type="mux" args="/out /a /b" /> without a parameter remap. The launched process is /opt/ros/noetic/lib/topic_tools/mux /out /a /b __name:=asdf. And the services are all under /mux and not /asdf.

Asked by rgov on 2022-06-13 17:53:09 UTC

Topic remapping in launch.xml is not working for topic_tools/mux node

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