[zeromq-dev] possible for XSUB to receive a message prior to XPUB getting subscription message?

[John Muehlhausen]

I have a process running zmq_poll on an XPUB socket as well as a bunch of
(very busy) non-zeromq fds.  zmq_init was called for '1' thread.  The
number and rate of XPUB outbound (published) messages is relatively low.

I'm pretty sure I observed the subscriber getting a published message well
before the zmq_poll notification (on the publisher side) that the
subscription message could be read.

Does this make sense?  What can go wrong on the XPUB side?  If other
clients have disappeared can this block reception of the next client's
subscription message?  Do I need to use the zmq_ctx_set method to increase
the priority of the zmq thread pool?  Does zmq_poll in any way prioritize
non-zmq fds in a way that would skip over ready zmq sockets?

Thanks for any thoughts or tips.
-John
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