[rabbitmq-discuss] TCP timeouts

[David.Corcoran at edftrading.com]

Hey Holger,

Thanks for the response. I've answered some of your queries below.

>
> A very interesting anomaly indeed, especially considering that it only
> seems to affect 1.5, not 1.4 or 1.6. However, as far as I can tell this
> behaviour can only occur with one CPU. I bet that David's test will run
> fine when he enables more cores and/or starts running "real" code in the
> process() method - meaning: code that creates garbage and doesn't just
> repeatedly busy-waits on a native method, which accidentally must also
> obey special synchronization rules. David, could you please try this if
it
> is not too inconvenient?

Unfortunately this happens in the real world too. The code with the while
loop was just to have a simple example that exhibited the same problem I
was having. Most of our cpu intensive code is manipulating matrices of
doubles so it uses full cpu and there is little or no garbage collection.
We use Colt (http://acs.lbl.gov/~hoschek/colt/) for most of it and it's so
optimised I'd be surprised if it had slow bits where other threads might
get a look in.

Also my machine is a quad core 3Ghz Xeon and this happens when just running
1 cpu intensive task.

> Ideally process() should run in a separate thread anyway so that the
> controlling thread can properly wait for a result or - more importantly -

> cancel the computation if necessary.
>

Process doing the calculations inline makes things conceptually a little
easier and each computation takes less than 30 (usually) so there's no need
to cancel them. Also even if it ran in a separate thread the heartbeat
thread wouldn't be scheduled because the computation thread would still be
too busy.

>
> Unfortunately this might not have the effect that one expects, as yield()
is:
>

I agree, yield is a complicated beast and I would never rely on it as a
solution. It was more just a way to illustrate the problem.

If RabbitMQ has configurable heartbeat timeouts this problem might
disappear. For example if you could up the disconnect timeout to 5 seconds
or more it's probably more likely the heartbeat thread would have had a
time slice by then. Still, the only real solution is to use Java6. :)

Regards,

Dave


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