[zeromq-dev] fd leak with dealer to dealer with tcp as transport

[Bill Torpey]

Hi Siva:

Bear in mind that zmq_disconnect is asynchronous (not well-documented IMO, but e.g., see https://github.com/zeromq/libzmq/issues/2759#issuecomment-389057453 <https://github.com/zeromq/libzmq/issues/2759#issuecomment-389057453>).  zmq_connect is also asynchronous in most cases (except inproc).  It also takes some time for fd’s to be reclaimed by OS.  

- Do fd’s eventually get reclaimed when system is idle?

- What state are fd’s in while application is running (e.g., lsof -p <PID> | grep TCP)?

- Have you tried using zmq_socket_monitor to trace what is happening under the covers?  

FWIW, you may want to reconsider the connect/send/disconnect approach - the overhead of connect/disconnect is considerable.  If you can connect once to each destination, life will be much simpler.

Good luck!

Bill


> On Nov 14, 2019, at 7:29 AM, donthamsetty sivaprasad via zeromq-dev <zeromq-dev at lists.zeromq.org> wrote:
> 
> Hi ,
> thanks for the response.
> I have multiple tasks(threads).
> Each task has tx and rx ZMQ DEALER sockets with bind to tcp addresses.
> Each guy before sending a packet to other one does zmq_connect , zmq_msg_send and zmq_disconnect. The reason for doing zmq_disconnect is sender's next packet could be to a different receiver other than the first one.
> 
> Now the first question is does zmq_disconnect destroys tcp sockets underneath or not ..( for that sender/receiver combo)??
> 
> When I did lsof it shows very huge number something like 50K..
> 
> Thanks
> Siva
> 
> 
> 
> On Thursday, November 14, 2019, 04:57:22 PM GMT+5:30, Arnaud Loonstra <arnaud at sphaero.org> wrote:
> 
> 
> On 14-11-2019 10:07, donthamsetty sivaprasad via zeromq-dev wrote:
> > Hi ,
> > I have DEALER sockets with tcp as transport.
> > Before sending each packet I do zmq_connect , zmq_msg_send and 
> > zmq_disconnect since same DEALER can talk to another dealer ( it is many 
> > to many communication ,but no load bancing or round robin)..
> > 
> > The system is crashing running out of file descriptors in the system..
> > Could you please help me..?
> > 
> > Thanks
> > Siva
> > 
> 
> Please show some code which demonstrates your problem. It sounds like 
> you are constantly creating new sockets without destroying them. In 
> general you first connect and then send the message. You only disconnect 
> if you need to (usually on destroy). Also have you read the zeromq 
> guide? It shows many examples.
> 
> Rg,
> 
> Arnaud
> 
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