[zeromq-dev] XREQ+XREP losing messages when HWM is hit

[Martin Lucina]

After some out of band discussion with Martin Hurton and Martin Sustrik, it
turns out that this is a bug, which was introduced by commit
84e0c7991a9b316ed571533abc628cc1175750a3 on 2 May 2010.

The intended behaviour of XREQ is that it should not drop messages, and
should block on ZMQ_HWM being hit just as REQ sockets do.

I will revert the problematic change on master; as a side effect devices
such as the queue device will not function correctly when ZMQ_HWM is
involved since the current implementation is naive and assumes that
zmq_send() will not block.

The fix is to reimplement the queue algorithm to use zmq_poll(). I will get
around to this eventually, in the mean time it is left as an excersize for
the reader :-)

-mato