ZeroMQ 在多线程应用程序中处理中断

Question

ZeroMQ 在多线程环境中的优雅退出

规格：ubuntu 16.04 和 c++11，libzmq：4.2.3

示例代码

static int s_interrupted = 0;
static void s_signal_handler (int signal_value)
{
    s_interrupted = 1;
    //some code which will tell main thread to exit
}

static void s_catch_signals (void)
{
    struct sigaction action;
    action.sa_handler = s_signal_handler;
    action.sa_flags = 0;
    sigemptyset (&action.sa_mask);
    sigaction (SIGINT, &action, NULL);
    sigaction (SIGTERM, &action, NULL);
}

static void Thread((zsock_t *pipe, void *)
{
    zmq::context_t context(1);
    zmq::socket_t requester1(context,ZMQ_DEALER);
    zmq::socket_t requester2(context,ZMQ_DEALER);
    requester1.connect(address1);
    requester2.connect(address2);
    zmq_pollitem_t items []=
        {{requester1,0,ZMQ_POLLIN,0},
        {requester2,0,ZMQ_POLLIN,0}};

    while(true)
    {
        zmq::message_t message;
        zmq::poll (items, 2, -1);

         if (items [0].revents & ZMQ_POLLIN) 
         {
             requester1.recv(&message);
         }
         if (items [1].revents & ZMQ_POLLIN) 
         {
             requester2.recv(&message);
         }
    }
}

int main()
{
    .
    //some code
    .

    zactor_t *actor = zactor_new (Threaded, nullptr);
    s_catch_signals();
    .
    //continue
    .
    //wait till thread finishes to exit

    return 0;
}

现在，当中断发生时，它将从主线程调用信号处理程序。我不知何故需要告诉线程（轮询器）从信号处理程序中退出。任何想法如何实现这一目标？

Answer 1

从 ZMQ 文档中，您有 2 种“惯用”方式来处理这个问题：

• Polling on a pipe，并在信号处理程序的管道上写入。

• Catching exception thrown in recv when a signal is sent。

经过测试，zmq::poll 似乎没有在 SIGINT 上抛出异常。 因此解决方案似乎是使用专用于关闭的套接字。 解决方案如下所示：

#include <iostream>
#include <thread>
#include <signal.h>
#include <zmq.hpp>
zmq::context_t* ctx;
static void s_signal_handler (int signal_value)
{
    std::cout << "Signal received" << std::endl;
    zmq::socket_t stop_socket(*ctx, ZMQ_PAIR);
    stop_socket.connect("inproc://stop_address");
    zmq::message_t msg("0", 1);
    stop_socket.send(msg);
    std::cout << "end sighandler" << std::endl;
}

static void s_catch_signals (void)
{
    struct sigaction action;
    action.sa_handler = s_signal_handler;
    action.sa_flags = 0;
    sigemptyset (&action.sa_mask);
    sigaction (SIGINT, &action, NULL);
    sigaction (SIGTERM, &action, NULL);
}

void thread(void)
{
    std::cout << "Thread Begin" << std::endl;
    zmq::context_t context (1);
    ctx = &context;
    zmq::socket_t requester1(context,ZMQ_DEALER);
    zmq::socket_t requester2(context,ZMQ_DEALER);
    zmq::socket_t stop_socket(context, ZMQ_PAIR);
    requester1.connect("tcp://127.0.0.1:36483");
    requester2.connect("tcp://127.0.0.1:36483");
    stop_socket.bind("inproc://stop_address");

    zmq_pollitem_t items []=
    {
        {requester1,0,ZMQ_POLLIN,0},
        {requester2,0,ZMQ_POLLIN,0},
        {stop_socket,0,ZMQ_POLLIN,0}
    };

    while ( true )
    {
        //  Blocking read will throw on a signal

        int rc = 0;
        std::cout << "Polling" << std::endl;
        rc = zmq::poll (items, 3, -1);

        zmq::message_t message;
        if(rc > 0)
        {
            if (items [0].revents & ZMQ_POLLIN)
            {
                requester1.recv(&message);
            }
            if (items [1].revents & ZMQ_POLLIN)
            {
                requester2.recv(&message);
            }
            if(items [2].revents & ZMQ_POLLIN)
            {
                std::cout << "message stop received " << std::endl;
                break;
            }
        }
    }
    requester1.setsockopt(ZMQ_LINGER, 0);
    requester2.setsockopt(ZMQ_LINGER, 0);
    stop_socket.setsockopt(ZMQ_LINGER, 0);
    requester1.close();
    requester2.close();
    stop_socket.close();
    std::cout << "Thread end" << std::endl;
}

int main(void)
{
    std::cout << "Begin" << std::endl;
    s_catch_signals ();
    zmq::context_t context (1);
    zmq::socket_t router(context,ZMQ_ROUTER);
    router.bind("tcp://127.0.0.1:36483");

    std::thread t(&thread);
    t.join();
    std::cout << "end join" << std::endl;

}

请注意，如果您不想将上下文共享给信号处理程序，您可以使用“ipc://...”。

Answer 2

如果您希望在处理信号时保留 ZMQ 的 Actor 模型的感觉，您可以使用 Linux 上的 signalfd 接口：signalfd manpage。这样，您可以使用 zmq poll 来等待信号被传递，而不是使用信号处理程序。

它还有一个额外的优势，即在处理通过文件描述符传递的信号时，您可以调用任何您喜欢的函数，因为您是同步处理它，而不是异步处理它。