Scala + ZMQ = Operation cannot be accomplished in current state

Question

I am trying to get a Scala program to communicate with a c++ program via zeromq by using the request-reply pattern. The scala program should send a request to the C++ program which replies.

However I see the error

org.zeromq.ZMQException: Operation cannot be accomplished in current state

But all I can find in the docu is that one has to read responses before sending a second request. In my case I am issuing a request, followed by a reading of the response (this is where the exception is thrown).

Code of the server:

#include "zmq.hpp"
#include <string>
#include <iostream>
#include <thread>

int main()
{
    zmq::context_t context(1);
    zmq::socket_t socket(context, ZMQ_REP);
    socket.bind("tcp://*:5555");


    while (1) {
        zmq::message_t request;
        socket.recv(&request);
        std::string requ = std::string(static_cast<char*>(request.data()), request.size());
        std::cout << requ << std::endl;

        //  Write response
        zmq::message_t req(2);
        memcpy((void *)req.data(), "ok", 5);
        socket.send(req);
    }
}

Code of the client:

import org.zeromq.ZMQ
import org.zeromq.ZMQ.{Context, Socket}

object Adapter {
  def main( args: Array[String] ) = {
    val context = ZMQ.context(1)
    val socket = context.socket(ZMQ.REQ)
    println { "Connecting to backend" }
    socket.connect("tcp://127.0.0.1:5555")
    val request = "1 1 1 1".getBytes()
    request(request.length - 1) = 0.toByte
    println { "Sending Request" }
    if (!socket.send(request, 0))
      println{ "could not send"}
    println { "Receiving Response" }
    val reply = socket.recv(0)
    println { "Received reply: " + new String(reply, 0, reply.length - 1) }
  }
}

The complete output of sbt:

OpenJDK 64-Bit Server VM warning: You have loaded library /tmp/jna7980154308052950568.tmp which might have disabled stack guard. The VM will try to fix the stack guard now.
It's highly recommended that you fix the library with 'execstack -c <libfile>', or link it with '-z noexecstack'.
Connecting to backend
Sending Request
Receiving Response
[error] (run-main-0) org.zeromq.ZMQException: Operation cannot be accomplished in current state
org.zeromq.ZMQException: Operation cannot be accomplished in current state
        at org.zeromq.ZMQ$Socket.raiseZMQException(ZMQ.java:448)
        at org.zeromq.ZMQ$Socket.recv(ZMQ.java:368)
        at ZeroMQActor$.main(ZeroMQExample.scala:56)
        at ZeroMQActor.main(ZeroMQExample.scala)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:606)
[trace] Stack trace suppressed: run last compile:run for the full output.
java.lang.RuntimeException: Nonzero exit code: 1
        at scala.sys.package$.error(package.scala:27)
[trace] Stack trace suppressed: run last compile:run for the full output.
[error] (compile:run) Nonzero exit code: 1
[error] Total time: 5 s, completed Jun 16, 2015 4:42:42 PM

Sbt pulls Scala 2.9.1 and akka-zeromq 2.0. I have installed zeromq 3.5 from source but I see the same behavior when I install the ubuntu package libzqm3-dev. One possible work-around is using JeroMQ, a pure java-based implementation of zmq, but I would prefer to depend on one zmq library in my whole stack rather than dealing with interop issues.

Thanks in advance.

Just for kicks, if you haven't done so already, try running a generic REQ/REP example in pure scala such as this one (look for the scala link to get scala code). If it runs, then switch the Scala server example code with the C++ server example code and try again. If it runs, there's a bug somewhere in your string/message handling. If it doesn't, there's likely a bug in your installation or language bindings. — Jason

Jason Jason · Accepted Answer · 2015-06-16T18:52:34

I believe

memcpy((void *)req.data(), "ok", 5);

should be

memcpy((void *)req.data(), "ok", 2);

... which could be enough to break message handling.

Scala + ZMQ = Operation cannot be accomplished in current state

1 Answers