Merge pull request zeromq#3996 from tarmo/xpub-unmatch

Problem: XPUB keeps matched pipes between failed non-blocking sends

RELICENSE/tarmo.md

@@ -0,0 +1,15 @@
+# Permission to Relicense under MPLv2 or any other OSI approved license chosen by the current ZeroMQ BDFL
+
+This is a statement by Tarmo Tänav that grants permission to
+relicense its copyrights in the libzmq C++ library (ZeroMQ) under the
+Mozilla Public License v2 (MPLv2) or any other Open Source Initiative
+approved license chosen by the current ZeroMQ BDFL (Benevolent
+Dictator for Life).
+
+A portion of the commits made by the Github handle "tarmo", with
+commit author "Tarmo Tänav <[email protected]>", are copyright of Tarmo Tänav.
+This document hereby grants the libzmq project team to relicense libzmq,
+including all past, present and future contributions of the author listed above.
+
+Tarmo Tänav
+2020/08/29

src/xpub.cpp

@@ -299,6 +299,9 @@ int zmq::xpub_t::xsend (msg_t *msg_)
 
     //  For the first part of multi-part message, find the matching pipes.
     if (!_more_send) {
+        // Ensure nothing from previous failed attempt to send is left matched
+        _dist.unmatch ();
+
         if (unlikely (_manual && _last_pipe && _send_last_pipe)) {
             _subscriptions.match (static_cast<unsigned char *> (msg_->data ()),
                                   msg_->size (), mark_last_pipe_as_matching,