CZMQ：无法接收消息

Question

我正在尝试编写一个简单的程序来演示使用 'libczmq' 的 Publisher/Subscriber 通信。虽然我可以通过 'zmsg_send' api 发送消息（或者我根据它的 return 值推测），但我无法通过 'zmsg_recv' 接收消息(blocking)API，可能收不到消息

#include "czmq.h"
int main (void)
{
  int rc;
  const char *ipc_file="ipc://tmp.socket";
  const char *str = "Hello World!!!";

  /*****************************************/
  /* Creating and binding publisher Socket */
  /*****************************************/
  zsock_t *pub_sock = zsock_new(ZMQ_PUB);
  assert(pub_sock!=NULL);
  rc = zsock_bind(pub_sock, ipc_file, NULL);
  assert(rc==0);

  /**************************************************/
  /* Creating and connecting with Subscriber Socket */
  /**************************************************/
  zsock_t *sub_sock = zsock_new(ZMQ_SUB);
  assert(sub_sock);
  rc = zsock_connect(sub_sock, ipc_file, NULL);
  assert(rc==0);

  /***************************************/
  /* Creating messager & Frame instances */
  /*         and sending message         */
  /***************************************/
  zmsg_t *msg = zmsg_new ();
  assert(msg!=NULL);
  zframe_t *frame = zframe_new (str, strlen(str));
  assert(frame!=NULL);
  zmsg_prepend(msg, &frame);
  printf("PUB : frame_count = %u, content_size = %d, msg_ptr = %p\n",
        zmsg_size (msg), zmsg_content_size(msg), msg);
  rc = zmsg_send(&msg, pub_sock);
  assert (rc == 0);
  printf("PUB : Message send successfully...\n");

  /********************************/
  /* Subscriber receiving message */
  /********************************/
  printf("SUB : Reading message...\n");
  msg = zmsg_recv(sub_sock);
  assert(msg!=NULL);
  printf("SUB : frame_count = %u, content_size = %d, msg_ptr = %p\n",
        zmsg_size (msg), zmsg_content_size(msg), msg);
  frame = zmsg_pop(msg);
  assert(frame!=NULL);
  printf("SUB : received in frame = \"%s\"\n", zframe_data (frame));

  zmsg_destroy (&msg);
  zframe_destroy (&frame);
  zsock_destroy (&sub_sock);
  zsock_destroy (&pub_sock);
  return 0;
}

下面是我构建和执行应用程序的方式。

user@debian:~/progs/czmq$ make
cc -Iczmq/include -ggdb   -c -o pub-sub-test.o pub-sub-test.c
gcc -L./czmq/src/.libs -lzmq -lczmq -lpthread pub-sub-test.o -o ../pub-sub-test
user@debian:~/progs/czmq$ ../pub-sub-test
PUB : frame_count = 1, content_size = 14, msg_ptr = 0x1653b10
PUB : Message send successfully...
SUB : Reading message...

订阅者从未阅读 'message'，请让我知道我在这里遗漏了什么。

Answer 1

默认情况下没有订阅 SUB 套接字。尝试使用需要订阅的变体：

zsock_t* zsock_new_sub (const char *endpoints, const char *subscribe)

或在 :

之后创建订阅

zsock_set_subscribe (void *zsock, const char *subscribe);

空字符串订阅一切

Answer 2

上面的程序有两个问题

@david 在之前的评论中指出 'zsock_set_subscribe' 缺失。
发布者在订阅者有机会连接之前发送消息，因此消息将丢失，订阅者将继续等待永远不会到来的消息。

解决方案：

在订阅者套接字后添加'zsock_set_subscribe' 已初始化。
在发布者和之前初始化订阅者在发布者之后立即添加一个小延迟（比如 1 秒）以便为订户提供足够的时间进行连接和最终收到消息。

CZMQ：无法接收消息

CZMQ : Unable to receive message

zeromq