Question

我正在尝试使用＆＃lib; libczmq＆＃39;编写一个简单的程序来演示发布者/订阅者通信。虽然我可以通过＆＃39; zmsg_send＆＃39;来发送消息。 api（或者根据其返回值推测），我无法通过＆＃39; zmsg_recv＆＃39;来接收消息。（阻塞）API，它可能无法接收消息。

#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;
}

以下是我构建和执行应用程序的方法。

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...

＆＃39;消息＆＃39;订阅者永远不会阅读，请告诉我这里缺少的内容。

Answer 1

默认情况下，SUB套接字上没有订阅。尝试使用订阅的变体：

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

或者在：

之后创建订阅

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

空字符串订阅所有内容。

Answer 2

上述程序存在两个问题。

缺少'zsock_set_subscribe'为@david在之前的评论中指出。
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发送的消息。

解决方案：

在订阅者套接字后添加'zsock_set_subscribe' 初始化。
在发布商和发布商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）为订户提供足够的时间连接和最终收到消息。

CZMQ：无法接收消息

2 个答案: