[zeromq-dev] reusing a mount point

Pieter Hintjens ph at imatix.com
Thu Nov 28 16:11:34 CET 2013


What OS are you using?

I've seen this symptom before, where a server cannot re-bind to a TCP
socket when there is an old client connection still connected to the
defunct socket. If you run netstat -a you'll see the socket in a wait
state, forever. When the client disconnects and restarts, it all works
again.

The problem is not solvable afaik at the lower levels. The new server
cannot force the socket out of a wait state (SO_REUSADDR does
nothing), and the client does not (afaik) get an error on the socket.

One solution is to detect the error using heartbeats, and then
explicitly close the socket at the client side, which frees the
server-side port for new connections.

I do not recall seeing the problem on Linux, only on AIX and Windows,
which is why I wonder what OS you're using.

It would be nice to add the heartbeating into ZMTP and libzmq if we
had budget to do that (and if this is in fact the problem).

-Pieter

On Thu, Nov 28, 2013 at 3:42 PM, Andrew Hume <andrew at research.att.com> wrote:
> a few months ago, i moved to czmq 3.2.3 and i’ve been quite happy except for
> one issue.
> i notice this rarely, so i’ve let it sit but now its become a nuisance.
>
> i have a stats_server which binds a PULL on port 46502.
> i have a hist_server which connects a PUSH to port 46502.
> ordinarily, the stats_server stays up for ever, while every now and then,
> we restart the hist_server process. so far, so good. and like always,
> we can start these servers in either order and it all works.
>
> what happens when we forget to restart the stats_server?
> the hist_server runs happily, sending stats over the channel on 46502.
> after (hours, days), we finally observe the stats_server is not up and we
> start it. it now fails because port 46502 “is in use”.
>
> this seems to be a bug to me.
>
> -----------------------
> Andrew Hume
> 949-707-1964 (VO and best)
> 732-420-0907 (NJ)
> andrew at research.att.com
>
>
>
>
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