socket.send() hangs forever when trying to send data to unbound socket with inproc protocol

[SlavikBaranov]

Here is minimal testcase:

package jmqtest;

import java.util.Arrays;
import org.jeromq.ZMQ;

public class JmqTest {

    public static String endpoint = "inproc://service1";
    //public static String endpoint = "tcp://127.0.0.1:10050";
    private static ZMQ.Context ctx = ZMQ.context(1);
    private static byte[] msg = new byte[] {1, 2, 3};

    private static final Runnable r = new Runnable() {

        @Override
        public void run() {
            ZMQ.Socket server = ctx.socket(ZMQ.REP);
            try {
                Thread.sleep(1000);
            } catch (InterruptedException ex) {
                System.out.println(ex);
            }
            server.bind(endpoint);
            byte[] recMsg = server.recv(0);
            boolean r = Arrays.equals(msg, recMsg);
            System.out.println(r ? "OK" : "Wrong message received");
            server.close();
        }

    };

    public static void main(String[] args) throws Exception {
        Thread t = new Thread(r);
        t.start();
        //Thread.sleep(1000);
        ZMQ.Socket client = ctx.socket(ZMQ.REQ);
        client.connect(endpoint);
        client.send(msg, 0);
        System.out.println("Waiting for thread to receive message...");
        t.join();
        client.close();
        ctx.term();
    }
}

When using jzmq instead of jeromq (change import in line 4), following exception is thrown:

Exception in thread "main" org.zeromq.ZMQException: Connection refused(0x3d)
at org.zeromq.ZMQ$Socket.connect(Native Method)
at jmqtest.JmqTest.main(JmqTest.java:37)

If bind() occurs before connect() (comment out lines 18-22 and uncomment line 35) everything works fine.

When using tcp transport instead of inproc (lines 8-9), late binding occurs and everything works fine too.

From the convenience point of view, late binding on inproc sockets would be ideal. From the interoperability point of view, exception on connect() should be thrown. In current state it's hard to diagnose, for example, misspelling of socket names in bind() and connect().

[miniway]

Thanks for the good catch.

An equivalent C code returns ECONNREFUSED and jeromq returns false.

But for the compatibility between jeromq and jzmq, jeromq should raise org.jeromq.ZMQException.

[SlavikBaranov]

Thank you for fixing it!

[cbeams]

I just tried @SlavikBaranov's JmqTest exactly as posted above and I get the same hanging behavior. However, I get it under both jeromq (0.3.4) and jzmq (3.0.1).

If, as suggested in the original description, I uncomment lines 18-22 and comment line 35, everything works as expected under both jeromq and jzmq.

With that said, it seems like this is actually the documented behavior. Per http://zguide.zeromq.org/page:all#Unicast-Transports (zeromq/libzmq#372):

The inter-thread transport, inproc, is a connected signaling transport. It is much faster than tcp or ipc. This transport has a specific limitation compared to tpc and icp: the server must issue a bind before any client issues a connect. This is something future versions of ØMQ may fix, but at present this defines how you use inproc sockets. We create and bind one socket and start the child threads, which create and connect the other sockets.

So I'm surprised that the desired behavior and/or the fix ever worked, as it seems to go directly against this documented limitation. Am I missing something?