[zeromq-dev] ZeroMQ how to troubleshoot the REQ-REP hang

[Jithendra Reddy]

Hi,

We have implemented a REQ-REP socket communication. In brief the
application does the following:
1. Client asks for a free tcp port through REQ socket
2. Server listens at REP socket, looks for  a free tcp port. Forks a child
process and runs ZeroMQ REP socket listening at the free port. Parent
process sends back this free port detail to client
3. Client then starts communicating to child process at the recieved port
using REQ-REP ZeroMQ socket

The above application has issues, if we do stress test. We are running
nearly 30 clients in one minute. Stress test works fine for a while (15-20
minutes) and then hangs.

We see that message is sent from REQ socket, but not recieved at REP
socket.
How to trouble shoot this issue?

We see that lsof is increasing as the stress test progresses. We do close
sockets in the application and also set linger to 0. Could the increased
lsof cause hang?

Your inputs to resolved the hang  and to troubleshoot the issue will be
helpful.

Regards
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