[zeromq-dev] problem with zmq::poll in ZMQ_REQ-ZMQ_ROUTER example

[Sandeep Joshi]

Hi All,

I am running zmq 3.2.3 and have some difficulty getting zmq::poll to work
with the frontend and backend sockets.

I modified the lbbroker.cpp example available in the zguide to move to the
client thread to a separate process in order to simulate the case where
multiple client processes connect to a multi-threaded server.

https://github.com/imatix/zguide/blob/master/examples/C%2B%2B/lbbroker.cpp

There are now two programs
Client : http://paste.ubuntu.com/7242473/
Multi-threaded Server : http://paste.ubuntu.com/7242472/

I deliberately added a "sleep(10") inside the worker_thread() to make it
pause and see if more than one worker threads are ever busy.  And I changed
the client to send multiple requests instead of just one.

When I ran the server followed by multiple instances of the client from
different terminals, I noticed that only one client's requests are
processed.  The other clients just seem to hang forever.

When I looked at "netstat", I noticed that the other clients do have TCP
connections in ESTABLISHED state.  From tshark, I found that there is some
initial TCP exchange for all clients but that zmq::poll only detects one
client's requests.  The other connected clients are just ignored.

The output of the server when more than one client is connected is as
follows:

The "5006" after the "hello" below is the process id of the client.  Notice
that only one client is being serviced even though more than one are active.

sent work req worker queue=20
Worker: 64F6-D716:hello5006
Worker sending resp: 64F6-D716:hello5006
Got worker resp: 8DD0-471C:queue=20
sent work req worker queue=20
Worker: 64F6-D716:hello5006
Worker sending resp: 64F6-D716:hello5006
Got worker resp: C4AA-55D1:queue=20
sent work req worker queue=20
Worker: 64F6-D716:hello5006
Worker sending resp: 64F6-D716:hello5006

What am I doing wrong ?

thanks
-Sandeep
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