[zeromq-dev] czmq vs forked process

Jay Rolette rolette at infinite.io
Wed Dec 21 16:49:02 CET 2016

I recently started using czmq and have run into a problem with the global
zmq context it uses when the process forks...

If the parent process does anything to cause the global context to be
created prior to forking, the child process is unable to send/recv
messages. That's not too surprising since zmq contexts aren't shareable
across processes, but I've been looking through the czmq code for a way to
destroy/recreate the global context in the child process and not finding an
obvious way to do that.

In older versions of czmq, it looks like I probably could have used zctx_*
calls to create a new context, but those were removed. Not seeing anything
similar in zsock_* or zsys_*.

Details about the behavior I'm seeing in the child process:

zmsg_send() returns success, but nothing is received on the server side. On
the client, the subsequent call to zmsg_recv() never returns.

This is on Ubuntu 14.04 LTS, czmq 4.0.1, libzmq 4.2 with pretty basic
REQ/REP sockets.

Is there anyway to stick with czmq for this or do I have to back off to
vanilla zmq?

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