REQ / REP模式中的ZeroMQ FiniteStateMachineException

Question

我有两个简单的组件，应该使用REQ / REP ZeroMQ模式相互通信。服务器（REP套接字）是使用pyzmq在Python中实现的：

import zmq

def launch_server():
    print "Launching server"
    with zmq.Context.instance() as ctx:
        socket = ctx.socket(zmq.REP)
        socket.bind('tcp://127.0.0.1:5555')

        while True:
            msg = socket.recv()
            print "EOM\n\n"

使用NetMQ库以C＃编写的客户端（REQ套接字）：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using NetMQ;


namespace PyNetMQTest
{
    class Program
    {

        static void Main(string[] args)
        {
            string msg;
            NetMQ.Sockets.RequestSocket socket = new NetMQ.Sockets.RequestSocket();
            socket.Connect("tcp://127.0.0.1:5555");
            for(int i=0; i<5; i++)
                socket.SendFrame("test_"+i);
        }
    }
}

通过与使用Python实现的REQ套接字进行通讯，Python Server实现已经过测试，可以正常工作。但是C＃REQ套接字在循环的第一次迭代中引发以下错误，并且任何消息都不会到达服务器：

NetMQ.dll中发生了'NetMQ.FiniteStateMachineException'类型的未处理异常。其他信息：Req.XSend-无法发送另一个请求

堆栈跟踪：

at NetMQ.Core.Patterns.Req.XSend(Msg& msg)
   at NetMQ.Core.SocketBase.TrySend(Msg& msg, TimeSpan timeout, Boolean more)
   at NetMQ.NetMQSocket.TrySend(Msg& msg, TimeSpan timeout, Boolean more)
   at NetMQ.OutgoingSocketExtensions.Send(IOutgoingSocket socket, Msg& msg, Boolean more)
   at NetMQ.OutgoingSocketExtensions.SendFrame(IOutgoingSocket socket, String message, Boolean more)
   at PyNetMQTest.Program.Main(String[] args) in d:\users\emes\documents\visual studio 2015\Projects\PyNetMQ Test\PyNetMQTest\Program.cs:line 20
   at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
   at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
   at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

这是我使用ZMQ的第一步，C＃代码来自库文档。是什么使代码引发此错误？

我在用：

• pyzmq 14.7
• NetMQ 3.3.3.4
• .NET 4.6

---

=====================解决方案====================

正如@somdoron在他的回答中所解释的，在这种情况下，两个套接字都需要经过完整的发送/接收周期才能被重用。事实上，用python实现的REP套接字也从未更改过它的状态，所以错误都在python和C＃代码中。这是固定代码：

REP插座

import zmq

def launch_server():
    print "Launching server"
    with zmq.Context.instance() as ctx:
        socket = ctx.socket(zmq.REP)
        socket.bind('tcp://127.0.0.1:5555')

        while True:
            msg = socket.recv()
            socket.send("reply to "+msg)
            print "EOM\n\n"

REQ插座

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using NetMQ;


namespace PyNetMQTest
{
    class Program
    {

        static void Main(string[] args)
        {

            NetMQ.Sockets.RequestSocket socket = new NetMQ.Sockets.RequestSocket();
            socket.Connect("tcp://127.0.0.1:5555");

            string msg, reply;

            while (true)
            {
                Console.WriteLine("Type message: ");
                msg = Console.ReadLine();
                Console.WriteLine("Sending : " + msg);
                socket.SendFrame(msg);
                reply = socket.ReceiveFrameString();
                Console.WriteLine("Received: " + reply + Environment.NewLine);
            }
        }
    }
}

Answer 1

Request和Response套接字是状态机，使用Request时，必须先发送，然后再调用Receive，才能连续调用5个Send。

与Response相反，您必须先致电Receive。

如果一侧仅发送而另一侧仅接收，则可以使用推拉模式而不是Req-Rep。如果需要双向通讯，也可以使用Dealer-Router。无论如何，似乎Req-Rep的用法不正确。