ZeroMQ with NORM - address already in use error was thrown on 2nd .bind() - why?

问题

I'm using ZeroMQ with NACK-Oriented Reliable Multicast ( NORM ) norm:// protocol. The documentation contains only a Python code, so here is my C++ code:

PUB Sender :

string sendHost         = "norm://2,127.0.0.1:5556";// <NormNodeId>,<addr:port>
string tag              = "MyTag";
string sentMessage      = "HelloWorld";
string fullMessage      = tag + sentMessage;

zmq::context_t *context = new zmq::context_t( 20 );

zmq::socket_t publisher( *context, ZMQ_PUB );
zmq_connect(  publisher, sendHost.c_str() );

zmq_send(     publisher,
              fullMessage.c_str(),
              fullMessage.size(),
              0
              );

SUB Receiver :

char   message[256];
string receiveHost      = "norm://1,127.0.0.1:5556";// <NormNodeId>,<addr:port>
string tag              = "MyTag";

zmq::context_t *context = new zmq::context_t( 20 );

zmq::socket_t   subscriber( *context, ZMQ_SUB );
zmq_bind(       subscriber, receiveHost.c_str() );
zmq_setsockopt( subscriber, ZMQ_SUBSCRIBE, tag.c_str(), tag.size() );

zmq_recv(       subscriber,
                message,
                256,
                0
                );

cout << bytesReceived << endl;
cout << message << endl;

The problem I'm facing is that according to the documentation both .bind() and .connect() are interchangeable.

In my case they both do a .bind(), which causes ZeroMQ to throw an error saying the second bind fails, due to address already in use error.

回答1:

... they both do a bind, which causes ZeroMQ to throw an error saying the second bind fails

Yes, this is a correct state to fail.

The first .bind() "takes ownership" of the port and this is an exclusive role.

The interchangeability of { .bind() | .connect() } is to be understood so that it does not matter which side .bind()-s and which one .connect()-s.

Until this moment, I saw no one interpreting this property in such a manner, that both sides would try to .connect() ( a non-existent .bind()-(not)-exposed Access Point ), the less to try to .bind() an already "occupied" port ( in case of residing on the same localhost ), or to remain in a nox-et-solitudo state, for the cases that either of the .bind()-s establishes such a .connect()-ready state on both ports on different localhost-s, which both after that remain in a silent solitude ( forever ), as there is ( and will be ) no attempt to make any .connect()-ion going live and operational.

No, you need just 1 .bind(), that may since that moment handle 0+ future .connect()-requests, arriving to establish a live-channel PUB/SUB, for any respective <transport-class> protocol, including the newly added norm://.

Anyways, welcome norm:// to the Family of ZeroMQ protocols.

Confused ?

May enjoy a further 5-seconds read
about the main conceptual differences in [ ZeroMQ hierarchy in less than a five seconds ] or other posts and discussions here.

来源：https://stackoverflow.com/questions/50753588/zeromq-with-norm-address-already-in-use-error-was-thrown-on-2nd-bind-why

标签

c++

zeromq

distributed-system