read() 似乎会阻塞，即使传递了 O_NONBLOCK 标志

Question

我正在尝试使用 UNIX 套接字编写聊天程序。它的工作原理应该与

nc -U '/tmp/...' -l

类似。 目前我只测试单向方法，但似乎无法使其工作。

我现在的问题是，服务器套接字的读取（显然）是阻塞的，我不知道为什么。 只需运行服务器套接字代码就应该打印出无限的“一个循环”循环，但是当您实际启动它时，它只会在读取时阻塞。

知道为什么吗？

服务器插座：

// standard includes
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
// includes for socket()
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/un.h>
// include for read()
#include <unistd.h>
// include for fnctl() (non-block)
#include <fcntl.h>

int main() {
  // variables
  int ret;
  int server_socket;
  struct sockaddr_un server_addr;
  char buffer[16]; //16byte transmission
  size_t byteSize;

  // create server_socket
  server_socket = socket(AF_UNIX, SOCK_DGRAM, 0);

  // make server socket non-blocking
    int status = fcntl(server_socket, F_SETFL, fcntl(server_socket, F_GETFL, 0) | O_NONBLOCK);

    if (status == -1){
        perror("calling fcntl");
    }

  // bind server_socket
  server_addr.sun_family = AF_UNIX;
  strcpy(server_addr.sun_path, "/tmp/bidirec.socket");
  ret =
      bind(server_socket, (struct sockaddr *)&server_addr, sizeof(server_addr));
  if (ret == -1) {
    perror("bind");
    exit(EXIT_FAILURE);
  }

  // masterloop
  while (1) {
        while(read(0, &buffer, 16) > 0) {
            write(server_socket, &buffer, 16);
            memset(&buffer, '0', sizeof(buffer));
            break;
        }
        printf("One loop\n");
    }
}

客户端套接字：

// standard includes
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// includes for socket()
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/un.h>
// include for write()
#include <unistd.h>

int main() {
  int ret;
  int client_socket;
  struct sockaddr_un client_addr;
  char buffer[16];

  // create client_socket
  client_socket = socket(AF_UNIX, SOCK_DGRAM, 0);

  // connect to server_socket
  client_addr.sun_family = AF_UNIX;
  strncpy(client_addr.sun_path, "/tmp/bidirec.socket",
          sizeof(client_addr.sun_path) - 1);
  ret = connect(client_socket, (struct sockaddr *)&client_addr,
                sizeof(client_addr));
  if (ret == -1) {
    fprintf(stderr, "The server is down.\n");
    exit(EXIT_FAILURE);
  }

  // masterloop
  while (1) {
      while(read(client_socket, &buffer, 16) > 0) {
            printf("%s", buffer);
            memset(&buffer, 0, sizeof(buffer));
            break;
        }
    }
}

Answer 1

答案：我不应该使套接字解除阻塞，而应该使“stdin”的 fd 解除阻塞。 第一次读取不依赖于实际的套接字。