On 01/17/2011 08:36 PM, Blaise Gassend wrote:
>> I somehow got dynparam get ... to work once, but i'm not sure what i
>> did, next time i tried it, it got stuck as usual. I tried to run
>> gdb/strace on it and it looks deadlocked waiting on semaphore. I also
>> looked through logs and it seems dead just before subscribing to
>> /dynamic_reconfigure_test_server/parameter_updates. Maybe python2.7 in
>> fedora 14 has something to do with that? The client never gets
>> subscribed>  never gets parameter_updates msg>  waits forever. Any
>> suggestions how I can debug it further?
> Can you try with python 2.6?
>
> Do other python nodes work well?
>
> Have you inserted prints in the dynamic reconfigure client code to try
> to figure out where it is getting stuck?
My point is getting it working under fedora 14 so python-2.7 is a given.

I was playing around a bit with simple python pub/sub examples and it looks like it is some kind of a race condition between multiple succeeding subscriptions under same 
nodehandle/prefix like /a/chatter1, /a/chatter2. It is not limited to dynamic_reconfigure.

It happens with both cpp and python publishers but only with a python subscriber. c++ subscriber always works fine.

I modified src/dynamic_reconfigure/client.py like this
          self._updates_sub      = self._get_subscriber('parameter_updates',...
+        rospy.sleep(1)
          self._descriptions_sub = self._get_subscriber('parameter_descriptions',...

and now it works.

I tested it with talker/listener tutorials modified with attached patch, and it randomly works ok, only with one topic or not at all.

v.