Hello Josh,

While trying to reproduce the delay build-up, I checked that the
behaviour you described is the one I observe, as long as my message
queue is positive.

However, I could reproduce the behaviour when the message queue is zero:
   ros::Subscriber sub = n.subscribe("chatter", 0, chatterCallback);

What is the intended behaviour in this case? I might have thought that
zero would disable the queue when I wrote the code earlier...
I guess the subscribe functions should document the semantic or flag
an error if the value is invalid.

Find my test programs attached. I'm postponing filing a ticket until I
understand if there is a mistake somewhere else than in my code :)

Best.

On Wed, Jan 5, 2011 at 7:38 PM, Josh Faust <jfaust@willowgarage.com> wrote:
>> In this case, I was getting message build-up even with when the
>> subscriber used a queue size of one. It seems that the teleop message
>> where small enough to accumulate in the TCP kernel or HW buffer and
>> not being discarded while the callback was running. This can be easily
>> identified by looking at the message timestamp. In our case, the
>> message age was increasing (obviously, you can only evaluate that on
>> machines with synchronised clocks).
>
> If you have a way to reproduce this, please file a ticket -- roscpp should
> be draining the sockets as quickly as possible whether or not your callbacks
> take a long time.  They should be totally decoupled.
> Josh
>
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-- 
Cedric Pradalier