[zeromq-dev] problem using last endpoint sockopt in pyzmq

[MinRK]

On Sat, Jan 12, 2013 at 3:33 PM, Chris Laws <clawsicus at gmail.com> wrote:

> Hi,
>
> I am trying to use a wildcard port in an effort to let the OS assign an
> ephemeral port. I then try to ascertain the actual endpoint by using the
> LAST_ENDPOINT socket option so that I can inform other apps of the real
> endpoint.
>
> This is along the lines of the suggestion here:
> http://lists.zeromq.org/pipermail/zeromq-dev/2012-October/018915.html
>
> A simple script which demonstrates the problem is located in this gist:
> https://gist.github.com/4520939
>
> The output I get when I run the script:
>
> Python version: 2.7.2 (default, Jun 20 2012, 16:23:33)  [GCC 4.2.1
> Compatible Apple Clang 4.0 (tags/Apple/clang-418.0.60)]
> zmq version: 3.2.2
> pyzmq version: 2.2dev
> Endpoint is tcp://192.168.1.2:*
> Traceback (most recent call last):
>   File "zmq_test.py", line 38, in <module>
>     router.getsockopt(zmq.LAST_ENDPOINT)
>   File "socket.pyx", line 394, in zmq.core.socket.Socket.getsockopt
> (zmq/core/socket.c:3915)
> zmq.core.error.ZMQError: Invalid argument
>
> zmq.LAST_ENDPOINT is an option listed in the constants module.
>
> Am I doing something wrong? Is there a better way to find the actual
> endpoint used when providing a wildcard port in the endpoint string to bind?
>

Running your script, I get:

Python version: 2.7.2 (default, Jun 20 2012, 16:23:33)  [GCC 4.2.1
Compatible Apple Clang 4.0 (tags/Apple/clang-418.0.60)]
zmq version: 3.2.2
pyzmq version: 2.2dev
Endpoint is tcp://192.168.1.193:*

So my guess is you just need to recompile pyzmq, and/or make sure it's up
to date.
Also, it looks like ZMQ_LAST_ENDPOINT doesn't actually do what you want it
to.
Perhaps this should be considered a libzmq bug?



>
> I am aware that pyzmq has the bind_to_random_port function but that does
> not really fit my need exactly as that could potentially block for some
> extended period of time.
>
In most cases it would likely be very short but I am trying to integrate
> ZMQ and Twisted together so I am trying to implement a solution that avoids
> blocking where ever possible.
>

How long do you think bind_to_random_port can block?  1ms would be an
unusually long time for that method to take (I've never seen it happen).
I would just use bind_to_random_port, rather than trying to fix a problem
that probably won't come up.

Two reasons:

1. bind will not take more than 1ms unless there are other, much more
severe performance issues going on
2. bind is a relatively rare call, so even if it were slow it generally
doesn't matter

-MinRK

>

>
> Regards,
> Chris
>
>
>
>
>
>
>
>
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>
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